Allowlist apexer for bp2build

This also introduces a workaround for the fact that
apexer depends on aapt2, but aapt2 doesn't build
with bp2build yet. Aapt2 is removed from apexer's
requirements during bp2build.

Bug: 204244290
Test: ./build/bazel/ci/bp2build.sh
Change-Id: I837597ce035c7d5c06e1a3957166583a7a94b5c7
diff --git a/genrule/genrule.go b/genrule/genrule.go
index 818e1bc..2a80563 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -266,7 +266,7 @@
 	var bazelOutputFiles android.Paths
 	exportIncludeDirs := map[string]bool{}
 	for _, bazelOutputFile := range filePaths {
-		bazelOutputFiles = append(bazelOutputFiles, android.PathForBazelOut(ctx, bazelOutputFile))
+		bazelOutputFiles = append(bazelOutputFiles, android.PathForBazelOutRelative(ctx, ctx.ModuleDir(), bazelOutputFile))
 		exportIncludeDirs[filepath.Dir(bazelOutputFile)] = true
 	}
 	g.outputFiles = bazelOutputFiles