loader: implement package maps #7649

Job	Run time
Build slim tarball	1m 32s
aarch64-linux: Cache V8 build	25s
x86_64-linux: with shared libraries	34s
aarch64-darwin: with shared libraries	35s
x86_64-darwin: with shared libraries	33s
aarch64-linux: with shared ${{ matrix.openssl.name }}	1s
	3m 40s

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