Don't merge apex variations with different UsePlatformApis

Merging apex variations with different UsePlatformApis results in
the presence of an extra apex with UsePlatformApis false changing
the behavior of an existing apex -> module dependency with
UsePlatformApis true, which can't be supported with incremental
analysis.  Don't merge apex variations with different UsePlatformApis
values, and add a _p suffix to the UsePlatformApis variation so they
can coexist.

Test: Test_mergeApexVariations
Bug: 372543712
Change-Id: I0e857a646a0449f87e4de6e6306ec921bc46fac1
diff --git a/android/apex.go b/android/apex.go
index 08c82eb..c2f73a9 100644
--- a/android/apex.go
+++ b/android/apex.go
@@ -105,6 +105,9 @@
 // thus wouldn't be merged.
 func (i ApexInfo) mergedName() string {
 	name := "apex" + strconv.Itoa(i.MinSdkVersion.FinalOrFutureInt())
+	if i.UsePlatformApis {
+		name += "_p"
+	}
 	return name
 }