libapexsupport: add INTRODUCED_IN(V)

and make the visibility explicit with guards.
- LLNDK symbols are visible to vendor (including vendor apex)
- Private symbols are visible to only system (not to system apex)

Bug: 362658565
Test: m
Change-Id: If4e80fb48a1e7eece3bb72fcd360a98817ecab49
2 files changed