fix(grit): fix matching function body

[arendjr]

Summary

We had an issue with matching function bodies in Grit queries that prevented metavariables from matching statements inside a function body. In fact, even the presence of a metavariable inside a snippet's function body would prevent the query from matching at all.

To fix it, I made sure JsMetavariable will be accepted in our grammar inside AnyJsStatement and updated the JS parser so it's accepted there.

Test Plan

Expanded test cases.

[codspeed-hq]

CodSpeed Performance Report

Merging #3810 will improve performances by 6.33%

_{Comparing arendjr:fix-matching-function-body (ac3c83d) with main (5f4a8c5)}

Summary

⚡ 1 improvements
✅ 106 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	arendjr:fix-matching-function-body	Change
⚡	jquery.min_16034160674129647344.js[cached]	28.7 ms	27 ms	+6.33%