feat(parser): parse Astro frontmatter

[ematipico]

Summary

Part of #6657

I added capabilities to the HTML parser to parse the Astro frontmatter, only when the HtmlFileSource has the Astro variant.

Test Plan

Added different test cases

[changeset-bot]

⚠️ No Changeset found

Latest commit: d25d18c

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[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	50611	50611	0
Passed	49294	49294	0
Failed	1317	1317	0
Panics	0	0	0
Coverage	97.40%	97.40%	0.00%

jsx/babel

Test result	main count	This PR count	Difference
Total	40	40	0
Passed	37	37	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.50%	92.50%	0.00%

symbols/microsoft

Test result	main count	This PR count	Difference
Total	6706	6706	0
Passed	2244	2244	0
Failed	4462	4462	0
Panics	0	0	0
Coverage	33.46%	33.46%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	822	822	0
Passed	731	731	0
Failed	91	91	0
Panics	0	0	0
Coverage	88.93%	88.93%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	18784	18784	0
Passed	14412	14412	0
Failed	4372	4372	0
Panics	0	0	0
Coverage	76.72%	76.72%	0.00%

[codspeed-hq]

CodSpeed Performance Report

Merging #6689 will not alter performance

_{Comparing feat/astro-frontmatter (d25d18c) with main (af78d6d)}

Summary

✅ 114 untouched benchmarks