Implement loading HTML from http.FileSystem #1615

Job	Run time
lint	24s
ubuntu-latest @ Go 1.21	32s
ubuntu-latest @ Go 1.21 -tags nomsgpack	41s
ubuntu-latest @ Go 1.21 -tags "sonic avx"	1m 5s
ubuntu-latest @ Go 1.21 -tags go_json	52s
ubuntu-latest @ Go 1.21 -race	13s
ubuntu-latest @ Go 1.22	35s
ubuntu-latest @ Go 1.22 -tags nomsgpack	39s
ubuntu-latest @ Go 1.22 -tags "sonic avx"	51s
ubuntu-latest @ Go 1.22 -tags go_json	52s
ubuntu-latest @ Go 1.22 -race	11s
macos-latest @ Go 1.21	45s
macos-latest @ Go 1.21 -tags nomsgpack	45s
macos-latest @ Go 1.21 -tags "sonic avx"	34s
macos-latest @ Go 1.21 -tags go_json	43s
macos-latest @ Go 1.21 -race	17s
macos-latest @ Go 1.22	37s
macos-latest @ Go 1.22 -tags nomsgpack	33s
macos-latest @ Go 1.22 -tags "sonic avx"	38s
macos-latest @ Go 1.22 -tags go_json	40s
macos-latest @ Go 1.22 -race	18s
	12m 45s

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