Python: Join-order improvement for DataFlowDispatch::TrackAttrReadInput

I was surprised to see that this predicate actually gets evaluated 3 times

- Pipeline standard for DataFlowDispatch::TrackAttrReadInput::start/2#67f26627@c15596yu was evaluated in 74 iterations totaling 165ms (delta sizes total: 113119).
- Pipeline standard for DataFlowDispatch::TrackAttrReadInput::start/2#67f26627@3459ejws was evaluated in 30 iterations totaling 76ms (delta sizes total: 32555).
- Pipeline standard for DataFlowDispatch::TrackAttrReadInput::start/2#67f26627@5ac22jwq was evaluated in 30 iterations totaling 108ms (delta sizes total: 32555).

It does however fit with it being used in exactly 3 places: https://github.com/search?q=repo%3Agithub%2Fcodeql+%2FattrReadTracker%5C%28%2F&type=code -- so I assume it's because each use forces a new evaluation. Although that's something we could look into solving, for now I'm just trying to fix the join-order.

Initial

```
Pipeline standard for DataFlowDispatch::TrackAttrReadInput::start/2#67f26627@3459ejws was evaluated in 30 iterations totaling 76ms (delta sizes total: 32555).
        7068090   ~0%    {2} r1 = SCAN Attributes::AttrRead#class#f6c3f431 OUTPUT In.0, In.0
                         {2}    | AND NOT `DataFlowDispatch::TrackAttrReadInput::start/2#67f26627#prev`(FIRST 2)
        3901178   ~5%    {2}    | SCAN OUTPUT In.1, In.1
        3901178   ~0%    {3}    | JOIN WITH `Attributes::AttrRef.getObject/0#dispred#d7cd0a97` ON FIRST 1 OUTPUT Rhs.1, Lhs.0, Lhs.1

          13615   ~1%    {2} r2 = JOIN r1 WITH `DataFlowDispatch::classTracker/1#d11f2237#reorder_1_0#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

             94   ~2%    {2} r3 = JOIN r1 WITH `DataFlowDispatch::superCallTwoArgumentTracker/2#d18be99f#reorder_2_0_1#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

          18846   ~1%    {2} r4 = JOIN r1 WITH `DataFlowDispatch::classInstanceTracker/1#d73ecef4#prev_delta_1#join_rhs` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

          32555   ~1%    {2} r5 = r2 UNION r3 UNION r4
                         return r5
```

==>

```
Pipeline standard for DataFlowDispatch::TrackAttrReadInput::start/2#67f26627@f2517jwq was evaluated in 30 iterations totaling 12ms (delta sizes total: 32704).
        186719  ~121%    {1} r1 = SCAN `DataFlowDispatch::classInstanceTracker/1#d73ecef4#prev_delta` OUTPUT In.1

        164342  ~158%    {1} r2 = SCAN `DataFlowDispatch::classTracker/1#d11f2237#reorder_1_0#prev_delta` OUTPUT In.0

            96    ~0%    {1} r3 = SCAN `DataFlowDispatch::superCallTwoArgumentTracker/2#d18be99f#reorder_2_0_1#prev_delta` OUTPUT In.0

        351157   ~80%    {1} r4 = r1 UNION r2 UNION r3
         88074   ~14%    {1}    | JOIN WITH `Attributes::AttrRef.getObject/0#dispred#d7cd0a97_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1
         41789   ~18%    {2}    | JOIN WITH Attributes::AttrRead#class#f6c3f431 ON FIRST 1 OUTPUT Lhs.0, Lhs.0
                         {2}    | AND NOT `DataFlowDispatch::TrackAttrReadInput::start/2#67f26627#prev`(FIRST 2)
         32883    ~2%    {2}    | SCAN OUTPUT In.1, In.1
                         return r4
```

AND

initial

```
Pipeline standard for DataFlowDispatch::TrackAttrReadInput::start/2#67f26627@c15596yu was evaluated in 74 iterations totaling 165ms (delta sizes total: 113119).
        17434622   ~0%    {2} r1 = SCAN Attributes::AttrRead#class#f6c3f431 OUTPUT In.0, In.0
                          {2}    | AND NOT `DataFlowDispatch::TrackAttrReadInput::start/2#67f26627#prev`(FIRST 2)
         9483976   ~4%    {2}    | SCAN OUTPUT In.1, In.1
         9483976   ~0%    {3}    | JOIN WITH `Attributes::AttrRef.getObject/0#dispred#d7cd0a97` ON FIRST 1 OUTPUT Rhs.1, Lhs.0, Lhs.1

           19258   ~1%    {2} r2 = JOIN r1 WITH `DataFlowDispatch::classInstanceTracker/1#d73ecef4#reorder_1_0#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

            1654   ~1%    {2} r3 = JOIN r1 WITH `DataFlowDispatch::superCallNoArgumentTracker/1#0a2e8a06#reorder_1_0#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

            1314   ~4%    {2} r4 = JOIN r1 WITH `DataFlowDispatch::clsArgumentTracker/1#47339327#reorder_1_0#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

              94   ~2%    {2} r5 = JOIN r1 WITH `DataFlowDispatch::superCallTwoArgumentTracker/2#d18be99f#reorder_2_0_1#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

           77217   ~0%    {2} r6 = JOIN r1 WITH `DataFlowDispatch::selfTracker/1#f157aa27#reorder_1_0#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

           13632   ~1%    {2} r7 = JOIN r1 WITH `DataFlowDispatch::classTracker/1#d11f2237#reorder_1_0#prev_delta` ON FIRST 1 OUTPUT Lhs.1, Lhs.2

          113169   ~0%    {2} r8 = r2 UNION r3 UNION r4 UNION r5 UNION r6 UNION r7
                          return r8
```
==>

```
Pipeline standard for DataFlowDispatch::TrackAttrReadInput::start/2#67f26627@d732e6yt was evaluated in 74 iterations totaling 31ms (delta sizes total: 113129).
        186719  ~150%    {1} r1 = SCAN `DataFlowDispatch::classInstanceTracker/1#d73ecef4#reorder_1_0#prev_delta` OUTPUT In.0

          1669    ~0%    {1} r2 = SCAN `DataFlowDispatch::superCallNoArgumentTracker/1#0a2e8a06#reorder_1_0#prev_delta` OUTPUT In.0

          3425   ~15%    {1} r3 = SCAN `DataFlowDispatch::clsArgumentTracker/1#47339327#prev_delta` OUTPUT In.1

            96    ~0%    {1} r4 = SCAN `DataFlowDispatch::superCallTwoArgumentTracker/2#d18be99f#reorder_2_0_1#prev_delta` OUTPUT In.0

        123310    ~0%    {1} r5 = SCAN `DataFlowDispatch::selfTracker/1#f157aa27#reorder_1_0#prev_delta` OUTPUT In.0

        164342  ~581%    {1} r6 = SCAN `DataFlowDispatch::classTracker/1#d11f2237#reorder_1_0#prev_delta` OUTPUT In.0

        479561   ~94%    {1} r7 = r1 UNION r2 UNION r3 UNION r4 UNION r5 UNION r6
        169424    ~2%    {1}    | JOIN WITH `Attributes::AttrRef.getObject/0#dispred#d7cd0a97_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1
        116290    ~0%    {2}    | JOIN WITH Attributes::AttrRead#class#f6c3f431 ON FIRST 1 OUTPUT Lhs.0, Lhs.0
                         {2}    | AND NOT `DataFlowDispatch::TrackAttrReadInput::start/2#67f26627#prev`(FIRST 2)
        113160    ~0%    {2}    | SCAN OUTPUT In.1, In.1
                         return r7
```

Author: RasmusWL

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll

@@ -876,7 +876,7 @@ private module TrackAttrReadInput implements CallGraphConstruction::Simple::Inpu
 
   predicate start(Node start, AttrRead attr) {
     start = attr and
-    attr.getObject() in [
+    pragma[only_bind_into](attr.getObject()) in [
         classTracker(_), classInstanceTracker(_), selfTracker(_), clsArgumentTracker(_),
         superCallNoArgumentTracker(_), superCallTwoArgumentTracker(_, _)
       ]