[Tool][Impeller] Make impellerc produce Vulkan and GLES shaders for Android. (#140976)

This should wait for some upstream work, just don't want to lose it locally for now. I'll switch this from draft and update the description when it's ready.

packages/flutter_tools/lib/src/build_system/targets/shader_compiler.dart

@@ -22,13 +22,13 @@ import '../build_system.dart';
 
 /// The output shader format that should be used by the [ShaderCompiler].
 enum ShaderTarget {
-  impellerAndroid('--runtime-stage-gles'),
-  impelleriOS('--runtime-stage-metal'),
-  sksl('--sksl');
+  impellerAndroid(<String>['--runtime-stage-gles', '--runtime-stage-vulkan']),
+  impelleriOS(<String>['--runtime-stage-metal']),
+  sksl(<String>['--sksl']);
 
-  const ShaderTarget(this.target);
+  const ShaderTarget(this.stages);
 
-  final String target;
+  final List<String> stages;
 }
 
 /// A wrapper around [ShaderCompiler] to support hot reload of shader sources.
@@ -177,7 +177,7 @@ class ShaderCompiler {
     final String shaderLibPath = _fs.path.join(impellerc.parent.absolute.path, 'shader_lib');
     final List<String> cmd = <String>[
       impellerc.path,
-      target.target,
+      ...target.stages,
       '--iplr',
       if (json)
         '--json',

packages/flutter_tools/test/general.shard/build_system/targets/android_test.dart

@@ -536,6 +536,7 @@ void main() {
       const FakeCommand(command: <String>[
         'HostArtifact.impellerc',
         '--runtime-stage-gles',
+        '--runtime-stage-vulkan',
         '--iplr',
         '--sl=out/flutter_assets/shader.glsl',
         '--spirv=out/flutter_assets/shader.glsl.spirv',

packages/flutter_tools/test/general.shard/build_system/targets/shader_compiler_test.dart

@@ -118,12 +118,13 @@ void main() {
     expect(fileSystem.file(outputPath).existsSync(), true);
   });
 
-  testWithoutContext('compileShader invokes impellerc for .frag files and opengl es', () async {
+  testWithoutContext('compileShader invokes impellerc for .frag files and Android', () async {
     final FakeProcessManager processManager = FakeProcessManager.list(<FakeCommand>[
       FakeCommand(
         command: <String>[
           impellerc,
           '--runtime-stage-gles',
+          '--runtime-stage-vulkan',
           '--iplr',
           '--sl=$outputPath',
           '--spirv=$outputPath.spirv',
@@ -292,6 +293,7 @@ void main() {
         command: <String>[
           impellerc,
           '--runtime-stage-gles',
+          '--runtime-stage-vulkan',
           '--iplr',
           '--sl=/.tmp_rand0/0.8255140718871702.temp',
           '--spirv=/.tmp_rand0/0.8255140718871702.temp.spirv',