Refactor lower_stmts

[camsteffen]

I have this change in #87688 but I think it deserves its own PR and a perf run.

Changes lower_stmt to lower_stmts and avoid creating a SmallVec for each ast::Stmt.

[rust-highfive]

r? @petrochenkov

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[camsteffen]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 28cf90d with merge 4e7f9014b4dc19485bb3ea6d3ebf68bab256b14f...

[camsteffen]

I don't know if 8 is optimal, but I think it is already used in the current implementation, in alloc_from_iter.

[bors]

☀️ Try build successful - checks-actions
Build commit: 4e7f9014b4dc19485bb3ea6d3ebf68bab256b14f (4e7f9014b4dc19485bb3ea6d3ebf68bab256b14f)

[rust-timer]

Queued 4e7f9014b4dc19485bb3ea6d3ebf68bab256b14f with parent 6fe0886, future comparison URL.

[rust-timer]

Finished benchmarking try commit (4e7f9014b4dc19485bb3ea6d3ebf68bab256b14f): comparison url.

Summary: This benchmark run did not return any significant changes.

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf -perf-regression

[camsteffen]

Neutral results I guess. Maybe it's easier to just close this PR.