feat(semantic): extend no_side_effects to include empty functions

[Dunqing]

Summary

• Mark functions with empty bodies and simple parameters as side-effect-free in Scoping::no_side_effects
• Covers function declarations, function expressions, and arrow functions (non-expression body)
• Allows Rolldown to use scoping.no_side_effects() as the single source of truth, eliminating its separate SymbolRefFlags::SideEffectsFreeFunction flag

Details

"Empty and simple params" means:

• Body has no statements and no directives
• All params are BindingIdentifier with no initializer (uses existing IsSimpleParameterList trait)
• No rest parameter
• Arrow functions must not have expression body (() => expr excluded)

Async and generator empty functions are included, consistent with esbuild and Rollup behavior.

Closes #20290

Test plan

• Added positive tests for empty function declarations, expressions, arrows, async, generators
• Added negative tests for non-empty bodies, non-simple parameters
• Updated existing test expectations that now correctly remove calls to empty functions
• cargo test -p oxc_minifier passes (470 tests)
• cargo test -p oxc_semantic --tests passes
• Clippy clean

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will not alter performance

✅ 53 untouched benchmarks
⏩ 3 skipped benchmarks¹

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_{Comparing feat/semantic-empty-fn-no-side-effects (192a994) with main (5474d0a)²}

Footnotes

1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (e704eae) during the generation of this report, so 5474d0a was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩