avm2: More optimizer improvements

[Lord-McSweeney]

We now have an optimizer pass to remove Nops from the final bytecode, and we make use of the vector's type for vector element accesses in the type-aware optimizer when we can.

My version of box2d doesn't use Vector, so here are the stats for a SWF using the Oimo physics library:

ConstructSuper -> Pop: 32.43%

ConstructProp -> ConstructSlot: 100%

FindPropStrict -> GetScriptGlobals: 35.08%
FindPropStrict -> GetOuterScope: 2.66%
FindPropStrict -> GetScopeObject: 62.25%

FindProperty -> GetScopeObject: 99.45%
FindProperty -> GetOuterScope: 0.54%

InitProperty -> SetSlotNoCoerce: 96.83%
InitProperty -> SetSlot: 0.92%
InitProperty -> CallMethod: 1.62%

SetPropertyStatic -> SetSlotNoCoerce: 69.3% (+2.35%)
SetPropertyStatic -> SetSlot: 11.72% (-1.61%)
SetPropertyStatic -> CallMethod: 18.68% (+1.54%)

GetPropertyStatic -> GetSlot: 93.46% (+0.33%)
GetPropertyStatic -> CallNative: 0.14%
GetPropertyStatic -> CallMethod: 5.3% (+0.11%)

CallProperty -> CallMethod: 59.54% (-1.71%)
CallProperty -> CallNative: 33.04% (+1.71%)

CallPropVoid -> CallMethod: 92.93% (+1.97%)
CallPropVoid -> CallNative: 3.24%

Coerce -> Nop: 95.17% (+24.04%)

CoerceD -> Nop: 99.3% (+3.14%)

CoerceU -> Nop: 26.83%

CoerceB -> Nop: 70%

CoerceI -> Nop: 87.33% (+1%)

AsType -> Nop: 100%

ReturnValue -> ReturnValueNoCoerce: 95.05% (+2.12%)