[flutter_tools] Migrate commands.shard/hermetic/doctor_test to null-safety and make hermetic (#107670)

Author: christopherfujino

packages/flutter_tools/lib/src/doctor.dart

@@ -320,12 +320,12 @@ class Doctor {
   Future<bool> diagnose({
     bool androidLicenses = false,
     bool verbose = true,
-    bool showColor = true,
     AndroidLicenseValidator? androidLicenseValidator,
     bool showPii = true,
     List<ValidatorTask>? startedValidatorTasks,
     bool sendEvent = true,
   }) async {
+    final bool showColor = globals.terminal.supportsColor;
     if (androidLicenses && androidLicenseValidator != null) {
       return androidLicenseValidator.runLicenseManager();
     }
@@ -644,7 +644,7 @@ class DoctorText {
 
   Future<String> _runDiagnosis(bool showPii) async {
     try {
-      await _doctor.diagnose(showColor: false, startedValidatorTasks: _validatorTasks, showPii: showPii, sendEvent: _sendDoctorEvent);
+      await _doctor.diagnose(startedValidatorTasks: _validatorTasks, showPii: showPii, sendEvent: _sendDoctorEvent);
       // Do not send the doctor event a second time.
       _sendDoctorEvent = false;
       final String text = _logger.statusText;