Bugfix: update color scheme references properly (#9103)

`CascadiaSettings::UpdateColorSchemeReferences` had two bugs in it:
1. we would never check/update the base layer
2. we would explicitly set the color scheme on a profile referencing the
   old name

This PR fixes both of those issues by checking/updating the base layer,
and ensuring that we check if a profile has an explicit reference before
updating it.

Since the affected code is in TSM, I also created an automated local
test.

## Validation Steps Performed
Bug repro steps.
Specifically tested [DHowett's scenario] too.
Test added.

Closes #9094

[DHowett's scenario]: #9094 (comment)

(cherry picked from commit 4251126)

src/cascadia/LocalTests_SettingsModel/ColorSchemeTests.cpp

@@ -35,6 +35,7 @@ namespace SettingsModelLocalTests
         TEST_METHOD(CanLayerColorScheme);
         TEST_METHOD(LayerColorSchemeProperties);
         TEST_METHOD(LayerColorSchemesOnArray);
+        TEST_METHOD(UpdateSchemeReferences);
 
         TEST_CLASS_SETUP(ClassSetup)
         {
@@ -290,4 +291,81 @@ namespace SettingsModelLocalTests
             VERIFY_ARE_EQUAL(ARGB(0, 7, 7, 7), scheme2->_Background);
         }
     }
+
+    void ColorSchemeTests::UpdateSchemeReferences()
+    {
+        const std::string settingsString{ R"json({
+                                                "defaultProfile": "Inherited reference",
+                                                "profiles": {
+                                                    "defaults": {
+                                                        "colorScheme": "Scheme 1"
+                                                    },
+                                                    "list": [
+                                                        {
+                                                            "name": "Explicit scheme reference",
+                                                            "colorScheme": "Scheme 1"
+                                                        },
+                                                        {
+                                                            "name": "Explicit reference; hidden",
+                                                            "colorScheme": "Scheme 1",
+                                                            "hidden": true
+                                                        },
+                                                        {
+                                                            "name": "Inherited reference"
+                                                        },
+                                                        {
+                                                            "name": "Different reference",
+                                                            "colorScheme": "Scheme 2"
+                                                        }
+                                                    ]
+                                                },
+                                                "schemes": [
+                                                    { "name": "Scheme 1" },
+                                                    { "name": "Scheme 2" },
+                                                    { "name": "Scheme 1 (renamed)" }
+                                                ]
+                                            })json" };
+
+        auto settings{ winrt::make_self<CascadiaSettings>(false) };
+        settings->_ParseJsonString(settingsString, false);
+        settings->_ApplyDefaultsFromUserSettings();
+        settings->LayerJson(settings->_userSettings);
+        settings->_ValidateSettings();
+
+        // update all references to "Scheme 1"
+        const auto newName{ L"Scheme 1 (renamed)" };
+        settings->UpdateColorSchemeReferences(L"Scheme 1", newName);
+
+        // verify profile defaults
+        Log::Comment(L"Profile Defaults");
+        VERIFY_ARE_EQUAL(newName, settings->ProfileDefaults().ColorSchemeName());
+        VERIFY_IS_TRUE(settings->ProfileDefaults().HasColorSchemeName());
+
+        // verify all other profiles
+        const auto& profiles{ settings->AllProfiles() };
+        {
+            const auto& prof{ profiles.GetAt(0) };
+            Log::Comment(prof.Name().c_str());
+            VERIFY_ARE_EQUAL(newName, prof.ColorSchemeName());
+            VERIFY_IS_TRUE(prof.HasColorSchemeName());
+        }
+        {
+            const auto& prof{ profiles.GetAt(1) };
+            Log::Comment(prof.Name().c_str());
+            VERIFY_ARE_EQUAL(newName, prof.ColorSchemeName());
+            VERIFY_IS_TRUE(prof.HasColorSchemeName());
+        }
+        {
+            const auto& prof{ profiles.GetAt(2) };
+            Log::Comment(prof.Name().c_str());
+            VERIFY_ARE_EQUAL(newName, prof.ColorSchemeName());
+            VERIFY_IS_FALSE(prof.HasColorSchemeName());
+        }
+        {
+            const auto& prof{ profiles.GetAt(3) };
+            Log::Comment(prof.Name().c_str());
+            VERIFY_ARE_EQUAL(L"Scheme 2", prof.ColorSchemeName());
+            VERIFY_IS_TRUE(prof.HasColorSchemeName());
+        }
+    }
 }

src/cascadia/TerminalSettingsModel/CascadiaSettings.cpp

@@ -874,10 +874,18 @@ winrt::Microsoft::Terminal::Settings::Model::ColorScheme CascadiaSettings::GetCo
 // - <none>
 void CascadiaSettings::UpdateColorSchemeReferences(const hstring oldName, const hstring newName)
 {
+    // update profiles.defaults, if necessary
+    if (_userDefaultProfileSettings &&
+        _userDefaultProfileSettings->HasColorSchemeName() &&
+        _userDefaultProfileSettings->ColorSchemeName() == oldName)
+    {
+        _userDefaultProfileSettings->ColorSchemeName(newName);
+    }
+
     // update all profiles referencing this color scheme
     for (const auto& profile : _allProfiles)
     {
-        if (profile.ColorSchemeName() == oldName)
+        if (profile.HasColorSchemeName() && profile.ColorSchemeName() == oldName)
         {
             profile.ColorSchemeName(newName);
         }