feat(fs): Export, test and document OnlyFilesFS (#3939) #1477

Job	Run time
lint	27s
ubuntu-latest @ Go 1.20	43s
ubuntu-latest @ Go 1.20 -tags nomsgpack	29s
ubuntu-latest @ Go 1.20 -tags "sonic avx"	1m 4s
ubuntu-latest @ Go 1.20 -tags go_json	49s
ubuntu-latest @ Go 1.20 -race	9s
ubuntu-latest @ Go 1.21	39s
ubuntu-latest @ Go 1.21 -tags nomsgpack	41s
ubuntu-latest @ Go 1.21 -tags "sonic avx"	55s
ubuntu-latest @ Go 1.21 -tags go_json	39s
ubuntu-latest @ Go 1.21 -race	16s
ubuntu-latest @ Go 1.22	29s
ubuntu-latest @ Go 1.22 -tags nomsgpack	39s
ubuntu-latest @ Go 1.22 -tags "sonic avx"	59s
ubuntu-latest @ Go 1.22 -tags go_json	41s
ubuntu-latest @ Go 1.22 -race	12s
macos-latest @ Go 1.20	42s
macos-latest @ Go 1.20 -tags nomsgpack	33s
macos-latest @ Go 1.20 -tags "sonic avx"	36s
macos-latest @ Go 1.20 -tags go_json	47s
macos-latest @ Go 1.20 -race	23s
macos-latest @ Go 1.21	45s
macos-latest @ Go 1.21 -tags nomsgpack	40s
macos-latest @ Go 1.21 -tags "sonic avx"	36s
macos-latest @ Go 1.21 -tags go_json	45s
macos-latest @ Go 1.21 -race	22s
macos-latest @ Go 1.22	46s
macos-latest @ Go 1.22 -tags nomsgpack	45s
macos-latest @ Go 1.22 -tags "sonic avx"	35s
macos-latest @ Go 1.22 -tags go_json	40s
macos-latest @ Go 1.22 -race	26s
	19m 12s

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