fs: support caller-supplied readFile() buffers #7412

Job	Run time
github.event_name == 'workflow_dispatch' && 'Skipped job' \|\| 'Build slim tarball'	0s
aarch64-linux: Cache V8 build	0s
${{ matrix.system }}: with shared libraries	-1s
aarch64-linux: with shared ${{ matrix.openssl.name }}	-1s
	-2s

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