Introduce BazelStringOrLabelFromProp.

Soong supports string properties, but they are overloaded, and can mean
one of three things:

* path reference
* module reference
* string literal

Bazel has different types: label and string attributes. Thus there needs
to be a way to categorize them correctly in bp2build.

This CL introduces a new function to be used on properties like
apex_key.private_key / apex_key.public_key, as well as
android_app.certificate / apex.certificate.

It is important to disambiguate the prop betenn a string literal
attribute or file/rule target label attribute, so this functions does
just that.  The new attributes are then further handled by their
respective macros (apex_key, android_binary, apex).

Bug: 253557437
Fixes: 253557437
Test: presubmits, new tests

Change-Id: Id8111cdd60d3aabcae7d17fe9da84d0ee3966023
diff --git a/apex/key.go b/apex/key.go
index 2b09f1d..0a7e80f 100644
--- a/apex/key.go
+++ b/apex/key.go
@@ -201,10 +201,10 @@
 
 type bazelApexKeyAttributes struct {
 	Public_key      bazel.LabelAttribute
-	Public_key_name bazel.LabelAttribute
+	Public_key_name bazel.StringAttribute
 
 	Private_key      bazel.LabelAttribute
-	Private_key_name bazel.LabelAttribute
+	Private_key_name bazel.StringAttribute
 }
 
 // ConvertWithBp2build performs conversion apexKey for bp2build
@@ -213,27 +213,11 @@
 }
 
 func apexKeyBp2BuildInternal(ctx android.TopDownMutatorContext, module *apexKey) {
-	var privateKeyLabelAttribute bazel.LabelAttribute
-	var privateKeyNameAttribute bazel.LabelAttribute
-	if module.properties.Private_key != nil {
-		m := String(module.properties.Private_key)
-		if android.SrcIsModule(m) == "" {
-			privateKeyNameAttribute.SetValue(android.BazelLabelForModuleSrcSingle(ctx, *module.properties.Private_key))
-		} else {
-			privateKeyLabelAttribute.SetValue(android.BazelLabelForModuleDepSingle(ctx, *module.properties.Private_key))
-		}
-	}
+	privateKeyLabelAttribute, privateKeyNameAttribute :=
+		android.BazelStringOrLabelFromProp(ctx, module.properties.Private_key)
 
-	var publicKeyLabelAttribute bazel.LabelAttribute
-	var publicKeyNameAttribute bazel.LabelAttribute
-	if module.properties.Public_key != nil {
-		m := String(module.properties.Public_key)
-		if android.SrcIsModule(m) == "" {
-			publicKeyNameAttribute.SetValue(android.BazelLabelForModuleSrcSingle(ctx, *module.properties.Public_key))
-		} else {
-			publicKeyLabelAttribute.SetValue(android.BazelLabelForModuleDepSingle(ctx, *module.properties.Public_key))
-		}
-	}
+	publicKeyLabelAttribute, publicKeyNameAttribute :=
+		android.BazelStringOrLabelFromProp(ctx, module.properties.Public_key)
 
 	attrs := &bazelApexKeyAttributes{
 		Private_key:      privateKeyLabelAttribute,