perf(isolated_declarations): reduce looping over statements

[overlookmotel]

Reduce number of loops over Program's statements.

1. transform_program_without_module_declaration constructed a temporary Vec and then iterated over it to generate the final Vec. Cut out the intermediate Vec.
2. transform_statements_on_demand created a Vec and then called retain on it to filter it down. Combine the Vec construction and filtering into a single loop.

The gain from (1) is larger, but only (2) will show up in our benchmark as it takes the transform_statements_on_demand path.

[overlookmotel]

• perf(isolated_declarations): reduce looping over statements #9393 👈 (View in Graphite)
• refactor(isolated_declarations): rename var #9390 : 1 other dependent PR (#9394 )
• refactor(isolated_declarations): use aliases ArenaBox / ArenaVec #9389
• ci(benchmarks): exclude parser from isolated declarations benchmark timing #9388
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #9393 will not alter performance

_{Comparing 02-23-perf_isolated_declarations_reduce_looping_over_statements (eca808a) with main (9baa756)}

Summary

✅ 33 untouched benchmarks

[overlookmotel]

Ha! Perf actually regresses a little. I'll have to look deeper.

[overlookmotel]

Now not negative perf effect, but not positive either. Never mind...