Disable source apex variant using apex_available_name

There are two versions of aosp extservices - one for Tplus and one for
Sminus. When prebuilts are active, the `contents` validation of both
variants of extservices bootclasspath fragments should be disabled to
account for BCP jar skew.

This CL adds ApexAvailableName to ApexInfo to achive that. If an
api_domain matching the ApexAvailableName has been selected in
`all_apex_contributions`, the source apex variants will be disabled.

Bug: 361771739

Test: lunch cf_x86_64_phone-next-userdebug
Test: m nothing with ag/28851886
Change-Id: I505a7ad8295c258e2eeef7f183669f7a75a1c88e

apex/apex.go

@@ -1073,6 +1073,7 @@ func (a *apexBundle) ApexInfoMutator(mctx android.TopDownMutatorContext) {
 		ApexContents:      []*android.ApexContents{apexContents},
 		TestApexes:        testApexes,
 		BaseApexName:      mctx.ModuleName(),
+		ApexAvailableName: proptools.String(a.properties.Apex_available_name),
 	}
 	mctx.WalkDeps(func(child, parent android.Module) bool {
 		if !continueApexDepsWalk(child, parent) {