bp2build: add allowlist for package-level conversions.

This CL adds the support for specifying lists of directories in
build/soong/android/bazel.go, which are then written into
out/soong/bp2build/MANIFEST. Using this configuration,
modules/directories can either default to bp2build_available: true or
false, while still retaining the ability to opt-in or out at the module level.

It also ensures that ConvertWithBp2Build returns true iff the module
type has a registered bp2build converter.

Test: go tests
Test: demo.sh full
Test: TreeHugger presubmits for bp2build and mixed builds.

Change-Id: I0e0f6f4b1b2ec045f2f1c338f7084defc5d23a55

android/register.go

@@ -174,7 +174,13 @@ func (ctx *Context) RegisterForBazelConversion() {
 		t.register(ctx)
 	}
 
-	RegisterMutatorsForBazelConversion(ctx, bp2buildPreArchMutators, bp2buildDepsMutators, bp2buildMutators)
+	bp2buildMutatorList := []RegisterMutatorFunc{}
+	for t, f := range bp2buildMutators {
+		ctx.config.bp2buildModuleTypeConfig[t] = true
+		bp2buildMutatorList = append(bp2buildMutatorList, f)
+	}
+
+	RegisterMutatorsForBazelConversion(ctx, bp2buildPreArchMutators, bp2buildDepsMutators, bp2buildMutatorList)
 }
 
 // Register the pipeline of singletons, module types, and mutators for