refactor(timings): separate data collection and presentation (#16282)

### What does this PR try to resolve?

The goal of this refactor is to separate data collection and
presentation,
so that we can replay an HTML report from log generated by
`-Zbuild-analysis`.

### How to test and review this PR?

Should have no user-facing change,
though I would encourage review to run `cargo build --timings`
and check if there is anything broken.

Author: epage

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

@@ -817,7 +817,11 @@ impl<'gctx> DrainState<'gctx> {
         }
 
         let time_elapsed = util::elapsed(build_runner.bcx.gctx.creation_time().elapsed());
-        if let Err(e) = self.timings.finished(build_runner, &errors.to_error()) {
+        if let Err(e) = self
+            .timings
+            .finished(build_runner, &errors.to_error())
+            .context("failed to render timing report")
+        {
             self.handle_error(&mut build_runner.bcx.gctx.shell(), &mut errors, e);
         }
         if build_runner.bcx.build_config.emit_json() {