loader: implement package maps #4406

Job	Run time
Build slim tarball	2m 8s
aarch64-linux: with shared libraries	19m 9s
aarch64-darwin: with shared libraries	21m 6s
x86_64-linux: with shared libraries	23m 51s
x86_64-darwin: with shared libraries	33m 59s
	1h 40m 13s

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