Generate info about the selected app variant in platform builds

This is a followup to aosp/2999198 and adds information about apps.

Each app will have an entry in this file with the following properties
- Name, mandatory
- Is_prebuilt, mandatory
- Prebuilt_info_file_path, optional

Implementation details
- Move prebuiltInfoProvider out of build/soong/apex to
  build/soong/android. This allows build/soong/java to use it.
- Introduce a new `prebuilt_info` prop to `android_app_set` and
  `android_app_import`
- All app module types will set a prebuiltInfoProvider in
  GenerateAndroidBuildActions, including the source app module types

Test: m nothing --no-skip-soong-tests
Test: m out/soong/prebuilt_info.json
Test: ls -l out/soong/prebuilt_info.json --human-readable
-rw------- 1 spandandas primarygroup 317K Mar 11 23:46 out/soong/prebuilt_info.json

Test: #modified trunk_staging.locally to select prebuilts of some
mainline apps. Spot-checked that `is_prebuilt` and
`prebuilt_info_file_path` get populated appropriately

Bug: 327480225
Change-Id: I5078e0ec26c9568194550909962b90111a5223f7

apex/apex_singleton.go

@@ -149,10 +149,10 @@ type apexPrebuiltInfo struct {
 }
 
 func (a *apexPrebuiltInfo) GenerateBuildActions(ctx android.SingletonContext) {
-	prebuiltInfos := []prebuiltInfo{}
+	prebuiltInfos := []android.PrebuiltInfo{}
 
 	ctx.VisitAllModules(func(m android.Module) {
-		prebuiltInfo, exists := android.SingletonModuleProvider(ctx, m, prebuiltInfoProvider)
+		prebuiltInfo, exists := android.SingletonModuleProvider(ctx, m, android.PrebuiltInfoProvider)
 		// Use prebuiltInfoProvider to filter out non apex soong modules.
 		// Use HideFromMake to filter out the unselected variants of a specific apex.
 		if exists && !m.IsHideFromMake() {