fix(es/parser): Fix let parsing in scripts to match spec

[zrosenbauer]

Description:

Fix for #8269

WIP - still need to tweak tests & verify running as strict: false

BREAKING CHANGE:

Related issue (if exists):

[changeset-bot]

⚠️ No Changeset found

Latest commit: 0e27a67

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[codspeed-hq]

CodSpeed Performance Report

Merging #9343 will degrade performances by 5.6%

_{Comparing zrosenbauer:fix/let-let-parser (0e27a67) with main (1454ab5)}

Summary

⚡ 2 improvements
❌ 4 regressions
✅ 172 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	zrosenbauer:fix/let-let-parser	Change
⚡	es/full/bugs-1	590.2 µs	530.9 µs	+11.17%
⚡	es/full/codegen/es2015	291.6 µs	282 µs	+3.41%
❌	es/visitor/base-perf/boxing_boxed	3.1 µs	3.2 µs	-3.66%
❌	es/visitor/base-perf/boxing_boxed_clone	2.3 µs	2.4 µs	-3.72%
❌	es/visitor/base-perf/boxing_unboxed	3.3 µs	3.4 µs	-4.29%
❌	es/visitor/base-perf/boxing_unboxed_clone	2.5 µs	2.6 µs	-5.6%

[mischnic]

This is fixed now by #9484