Bp2build: handle embedded structs as blueprint

For structs that are embedded, Blueprint does not nest under the
embedded name, flattening them into the original struct for blueprint
files (e.g.
9fd2ed93df:proptools/unpack_test.go;l=402-431;drc=3adb2409648d6f8b25354ac47f083dae87731f10).
We should do the same for bp2build.

This will also allow us to embed structs for bp2build conversion
allowing more reuse.

Test: go test bp2build tests
Change-Id: I9ce088462adaf59bffa80bea76cd488e31f98e9d

bp2build/testing.go

@@ -148,7 +148,18 @@ type nestedProps struct {
 	Nested_prop string
 }
 
+type EmbeddedProps struct {
+	Embedded_prop string
+}
+
+type OtherEmbeddedProps struct {
+	Other_embedded_prop string
+}
+
 type customProps struct {
+	EmbeddedProps
+	*OtherEmbeddedProps
+
 	Bool_prop     bool
 	Bool_ptr_prop *bool
 	// Ensure that properties tagged `blueprint:mutated` are omitted
@@ -246,7 +257,17 @@ func customDefaultsModuleFactory() android.Module {
 	return m
 }
 
+type EmbeddedAttr struct {
+	Embedded_attr string
+}
+
+type OtherEmbeddedAttr struct {
+	Other_embedded_attr string
+}
+
 type customBazelModuleAttributes struct {
+	EmbeddedAttr
+	*OtherEmbeddedAttr
 	String_prop      string
 	String_list_prop []string
 	Arch_paths       bazel.LabelListAttribute
@@ -275,6 +296,10 @@ func customBp2BuildMutator(ctx android.TopDownMutatorContext) {
 			String_list_prop: m.props.String_list_prop,
 			Arch_paths:       paths,
 		}
+		attrs.Embedded_attr = m.props.Embedded_prop
+		if m.props.OtherEmbeddedProps != nil {
+			attrs.OtherEmbeddedAttr = &OtherEmbeddedAttr{Other_embedded_attr: m.props.OtherEmbeddedProps.Other_embedded_prop}
+		}
 
 		props := bazel.BazelTargetModuleProperties{
 			Rule_class: "custom",