Add GetEmbeddedPrebuilt and IsModulePrebuilt

Dedups the many repetitions of the code to obtain a *Prebuilt from a
module.

Bug: 177892522
Test: m nothing
Change-Id: I1ededbe9ee79e89ea6dd8882dfee4be0bf0b51b7
diff --git a/dexpreopt/config.go b/dexpreopt/config.go
index 8a656ed..7397919 100644
--- a/dexpreopt/config.go
+++ b/dexpreopt/config.go
@@ -404,14 +404,14 @@
 		if parent == ctx.Module() && ctx.OtherModuleDependencyTag(child) == Dex2oatDepTag {
 			// Found the source module, or prebuilt module that has replaced the source.
 			dex2oatModule = child
-			if p, ok := child.(android.PrebuiltInterface); ok && p.Prebuilt() != nil {
+			if android.IsModulePrebuilt(child) {
 				return false // If it's the prebuilt we're done.
 			} else {
 				return true // Recurse to check if the source has a prebuilt dependency.
 			}
 		}
 		if parent == dex2oatModule && ctx.OtherModuleDependencyTag(child) == android.PrebuiltDepTag {
-			if p, ok := child.(android.PrebuiltInterface); ok && p.Prebuilt() != nil && p.Prebuilt().UsePrebuilt() {
+			if p := android.GetEmbeddedPrebuilt(child); p != nil && p.UsePrebuilt() {
 				dex2oatModule = child // Found a prebuilt that should be used.
 			}
 		}