Support + prefix in lint/useFilenamingConvention rule

[Conaclos]

Discussed in #2244

^{Originally posted by minht11 March 30, 2024}
Sveltekit routes are defined something with + prefix something like "routes/+page.ts", trying to use Biome useFilenamingConvention rule seems to be incompatible

"useFilenamingConvention": {
	"level": "error",
	"options": {
		"filenameCases": ["kebab-case", "export", "PascalCase"]
	}
}
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