Ensure that integration tests are actually being run (#3857)

Many of our integration tests weren't actually being run on CI because they were in the wrong place and/or missing the driver file, and it seems we've just never noticed. This makes a number of changes:
- Ensures that all packages with integration tests also have a driver file in the right location.
  - Also standardizes the format of those files, as the boilerplate `main()` is available in `integration_test`.
- Ensures that all integration_test directories are in the right place.
  - In a couple of places, removes a duplicate copy of the integration test file.
- Makes it an error for a plugin that's not excluded to not have integration tests, so this can't easily happen again.
- Adds logging of what's being run and skipped, so if something does go wrong in the future it's easy to determine what from the logs.
  - Excludes `*_platform_interface` since the logging was (potentially confusingly) reporting that they were skipped because they don't support the current platform. Skipping them is correct, just not for that reason.
- Excludes the plugins that currently have no integration tests, with references to issues about adding them.

Fixes https://github.com/flutter/flutter/issues/81929

script/tool/test/drive_examples_command_test.dart

@@ -55,6 +55,7 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -100,6 +101,7 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -143,6 +145,25 @@ void main() {
           throwsA(const TypeMatcher<ToolExit>()));
     });
 
+    test('a plugin without any integration test files is reported as an error',
+        () async {
+      createFakePlugin('plugin',
+          withExtraFiles: <List<String>>[
+            <String>['example', 'lib', 'main.dart'],
+          ],
+          isAndroidPlugin: true,
+          isIosPlugin: true);
+
+      final Directory pluginExampleDirectory =
+          mockPackagesDir.childDirectory('plugin').childDirectory('example');
+
+      createFakePubspec(pluginExampleDirectory, isFlutter: true);
+
+      await expectLater(
+          () => runCapturingPrint(runner, <String>['drive-examples']),
+          throwsA(const TypeMatcher<ToolExit>()));
+    });
+
     test(
         'driving under folder "test_driver" when targets are under "integration_test"',
         () async {
@@ -168,6 +189,7 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -223,6 +245,8 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
+          'Not supported for the target platform; skipping.',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -255,6 +279,7 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -300,6 +325,8 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
+          'Not supported for the target platform; skipping.',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -332,6 +359,7 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -379,6 +407,8 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
+          'Not supported for the target platform; skipping.',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -411,6 +441,7 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -460,6 +491,8 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
+          'Not supported for the target platform; skipping.',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -492,6 +525,7 @@ void main() {
       expect(
         output,
         orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
           '\n\n',
           'All driver tests successful!',
         ]),
@@ -535,6 +569,29 @@ void main() {
         'drive-examples',
       ]);
 
+      expect(
+        output,
+        orderedEquals(<String>[
+          '\n==========\nChecking plugin...',
+          'Not supported for the target platform; skipping.',
+          '\n\n',
+          'All driver tests successful!',
+        ]),
+      );
+
+      print(processRunner.recordedCalls);
+      // Output should be empty since running drive-examples --macos with no macos
+      // implementation is a no-op.
+      expect(processRunner.recordedCalls, <ProcessCall>[]);
+    });
+
+    test('platform interface plugins are silently skipped', () async {
+      createFakePlugin('aplugin_platform_interface');
+
+      final List<String> output = await runCapturingPrint(runner, <String>[
+        'drive-examples',
+      ]);
+
       expect(
         output,
         orderedEquals(<String>[