fix(useNamingConvention): handle custom conventions on abstract classes

[Conaclos]

Summary

Fix #1725 (comment)

This PR fixes two bugs:

• We erroneously rejected a valid configuration
• We didn't set the abstract modifier flag for abstract classes

Test Plan

I added a non-regression test.

[github-actions]

Parser conformance results on

js/262

Test result	main count	This PR count	Difference
Total	48353	48353	0
Passed	47156	47156	0
Failed	1197	1197	0
Panics	0	0	0
Coverage	97.52%	97.52%	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	6556	6556	0
Passed	2203	2203	0
Failed	4353	4353	0
Panics	0	0	0
Coverage	33.60%	33.60%	0.00%

ts/babel

Test result	main count	This PR count	Difference
Total	670	670	0
Passed	598	598	0
Failed	72	72	0
Panics	0	0	0
Coverage	89.25%	89.25%	0.00%

ts/microsoft

Test result	main count	This PR count	Difference
Total	18290	18290	0
Passed	14018	14018	0
Failed	4272	4272	0
Panics	0	0	0
Coverage	76.64%	76.64%	0.00%

[codspeed-hq]

CodSpeed Performance Report

Merging #3473 will improve performances by 6.7%

_{Comparing conaclos/useNamingConvention-abstract-class (78b1694) with main (ff6a9a1)}

Summary

⚡ 1 improvements
✅ 103 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	conaclos/useNamingConvention-abstract-class	Change
⚡	react.production.min_3378072959512366797.js[cached]	2 ms	1.9 ms	+6.7%