docs: language creation

[ematipico]

Summary

This PR adds some documentation and instructions around our grammar.

It also refactors the code gen to have everything inside LanguageKind, which means that when adding a new language, the developer just need update the methods inside the impl LangaugeKind, nothing else (other then creating the KindSrc)

Test Plan

CI should pass. Proof read

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[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	49701	49701	0
Passed	48721	48721	0
Failed	980	980	0
Panics	0	0	0
Coverage	98.03%	98.03%	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	6322	6322	0
Passed	2036	2036	0
Failed	4286	4286	0
Panics	0	0	0
Coverage	32.20%	32.20%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	662	662	0
Passed	593	593	0
Failed	69	69	0
Panics	0	0	0
Coverage	89.58%	89.58%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	17646	17646	0
Passed	13439	13439	0
Failed	4205	4205	0
Panics	2	2	0
Coverage	76.16%	76.16%	0.00%

[arendjr]

Love it! This will definitely help to smooth the process for additional languages.