Add support for variant_prepend properties in bp2build for cc library

Some properties in soong are marked "variant_prepend", which means
in bp2build output, variant properties(select ...) should come before
general properties.
Prepend property is added in StringListAttribute
stuct so that bp2build can handlle variant_prepend properly, if
Prepend is properly set in different module logics.
This change also coordinates cc library with Prepend.
Coordination with other module types will be in separate CLs.

Bug: 261644490
Test: TestCcLibraryHeadersSimple,
TestCcLibraryHeadersArchAndTargetExportSystemIncludes and TH

Change-Id: I3b61c491c54bbe91ba9aa2af9b4c84193c91ae7f