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

java/app_import.go

@@ -150,6 +150,11 @@ type AndroidAppImportProperties struct {
 	// If unspecified, follows the naming convention that the source module of
 	// the prebuilt is Name() without "prebuilt_" prefix
 	Source_module_name *string
+
+	// Path to the .prebuilt_info file of the prebuilt app.
+	// In case of mainline modules, the .prebuilt_info file contains the build_id that was used
+	// to generate the prebuilt.
+	Prebuilt_info *string `android:"path"`
 }
 
 func (a *AndroidAppImport) IsInstallable() bool {
@@ -413,6 +418,14 @@ func (a *AndroidAppImport) generateAndroidBuildActions(ctx android.ModuleContext
 	}
 	android.CollectDependencyAconfigFiles(ctx, &a.mergedAconfigFiles)
 
+	providePrebuiltInfo(ctx,
+		prebuiltInfoProps{
+			baseModuleName: a.BaseModuleName(),
+			isPrebuilt:     true,
+			prebuiltInfo:   a.properties.Prebuilt_info,
+		},
+	)
+
 	// TODO: androidmk converter jni libs
 }