feat(shorebird_cli): add listBranches to Git

packages/shorebird_cli/lib/src/git.dart

@@ -87,6 +87,29 @@ class Git {
     }
   }
 
+  /// List all branches in the git repository located at [directory] that match
+  /// the [pattern].
+  Future<String> listBranches({
+    required String directory,
+    required String pattern,
+  }) async {
+    final arguments = ['branch', '--all', '--list', pattern];
+    final result = await process.run(
+      executable,
+      arguments,
+      workingDirectory: directory,
+    );
+    if (result.exitCode != 0) {
+      throw ProcessException(
+        executable,
+        arguments,
+        '${result.stderr}',
+        result.exitCode,
+      );
+    }
+    return '${result.stdout}'.trim();
+  }
+
   /// Prunes stale remote branches from the repository at [directory]
   /// associated with [name].
   Future<void> remotePrune({

packages/shorebird_cli/test/src/git_test.dart

@@ -189,6 +189,45 @@ void main() {
       });
     });
 
+    group('listBranches', () {
+      const directory = 'repository';
+      const pattern = 'pattern';
+      const output = '''
+* main
+  stable
+  remotes/origin/HEAD -> origin/main''';
+      test('executes correct command', () async {
+        when(() => processResult.stdout).thenReturn(output);
+        await expectLater(
+          runWithOverrides(
+            () => git.listBranches(pattern: pattern, directory: directory),
+          ),
+          completion(equals(output)),
+        );
+        verify(
+          () => process.run(
+            'git',
+            ['branch', '--all', '--list', pattern],
+            workingDirectory: directory,
+          ),
+        ).called(1);
+      });
+
+      test('throws ProcessException if process exits with error', () async {
+        const error = 'oops';
+        when(() => processResult.exitCode).thenReturn(ExitCode.software.code);
+        when(() => processResult.stderr).thenReturn(error);
+        expect(
+          () => runWithOverrides(
+            () => git.listBranches(pattern: pattern, directory: directory),
+          ),
+          throwsA(
+            isA<ProcessException>().having((e) => e.message, 'message', error),
+          ),
+        );
+      });
+    });
+
     group('remotePrune', () {
       const directory = './output';
       const name = 'origin';