Allow platform modules to link to vendor public libraries

Normally, when building with VNDK, platform modules are not allowed to
link against vendor libraries, because the ABI of the vendor libraries
are not guaranteed to be stable and may differ across multiple vendor
images.

However, the vendor public libraries are the exceptions. Vendor public
libraries are vendor libraries that are exposed to 3rd party apps and
listed in /vendor/etc/public.libraries.txt. Since they are intended to
be exposed to public, their ABI stability is guaranteed (by definition,
though it is up to the vendor to actually guarantee it).

This change provides a way to make a vendor lib as public by defining a
module of type 'vendor_public_library' with a map file that enumerates
public symbols that are publicized:

cc_library {
   name: "libvendor",
   proprietary: true,
   ...
}

vendor_public_library {
   name: "libvendor",
   symbol_file: "libvendor.map.txt",
}

This defines a stub library module named libvendor.vendorpublic from the
map file. `shared_libs: ["libvendor"]` is redirected to the stub library
when it is from the outside of the vendor partition.

Bug: 74275385
Test: m -j
Test: cc_test.go passes
Change-Id: I5bed94d7c4282b777632ab2f0fb63c203ee313ba