refactor(timings): reuse timing metric collection logic between --timings and -Zbuild-analysis (#16497)

Close #16474.

## What this PR addresses

As described in the issue above, `cargo build --timings` and `cargo
report timings` each had its own metric collection logic. Because `cargo
report timings` will supersede `cargo build --timings`, this PR try to
remove redundant logics from `core/compiler/timings/mod.rs`.

## Review points

- I'm not sure if it's appropriate to modify logger for refactoring.
However, logs emitted inside `core/compiler/timings/mod.rs` alone is not
enough for `prepare_context_from_iter()` to properly replay the build so
I think this is an appropriate way.

Author: weihanglo

src/cargo/core/compiler/job_queue/mod.rs

@@ -391,7 +391,7 @@ impl<'gctx> JobQueue<'gctx> {
         JobQueue {
             queue: DependencyQueue::new(),
             counts: HashMap::new(),
-            timings: Timings::new(bcx, &bcx.roots),
+            timings: Timings::new(bcx),
         }
     }
 
@@ -974,13 +974,11 @@ impl<'gctx> DrainState<'gctx> {
 
         match is_fresh {
             true => {
-                self.timings.add_fresh();
                 // Running a fresh job on the same thread is often much faster than spawning a new
                 // thread to run the job.
                 doit(Some(&self.diag_dedupe));
             }
             false => {
-                self.timings.add_dirty();
                 scope.spawn(move || doit(None));
             }
         }

src/cargo/core/compiler/mod.rs

@@ -1173,8 +1173,8 @@ fn add_allow_features(build_runner: &BuildRunner<'_, '_>, cmd: &mut ProcessBuild
 ///
 /// [`--error-format`]: https://doc.rust-lang.org/nightly/rustc/command-line-arguments.html#--error-format-control-how-errors-are-produced
 fn add_error_format_and_color(build_runner: &BuildRunner<'_, '_>, cmd: &mut ProcessBuilder) {
-    let enable_timings = build_runner.bcx.gctx.cli_unstable().section_timings
-        && (build_runner.bcx.build_config.timing_report || build_runner.bcx.logger.is_some());
+    let enable_timings =
+        build_runner.bcx.gctx.cli_unstable().section_timings && build_runner.bcx.logger.is_some();
     if enable_timings {
         cmd.arg("-Zunstable-options");
     }