Add some trace logging concerning which schemes are in use (#6803)

## Summary of the Pull Request

Let's try and figure out just how many people are actually using Solarized. I emailed @DHowett about this a week ago, but otherwise we don't really have any other tasks for this.

## PR Checklist
* [x] I work here
* [n/a] Requires documentation to be updated

src/cascadia/TerminalApp/CascadiaSettings.cpp

@@ -718,3 +718,30 @@ std::string CascadiaSettings::_ApplyFirstRunChangesToSettingsTemplate(std::strin
 
     return finalSettings;
 }
+
+// Method Description:
+// - Lookup the color scheme for a given profile. If the profile doesn't exist,
+//   or the scheme name listed in the profile doesn't correspond to a scheme,
+//   this will return `nullptr`.
+// Arguments:
+// - profileGuid: the GUID of the profile to find the scheme for.
+// Return Value:
+// - a non-owning pointer to the scheme.
+const ColorScheme* CascadiaSettings::GetColorSchemeForProfile(const GUID profileGuid) const
+{
+    auto* profile = FindProfile(profileGuid);
+    if (!profile)
+    {
+        return nullptr;
+    }
+    auto schemeName = profile->GetSchemeName().has_value() ? profile->GetSchemeName().value() : L"\0";
+    auto scheme = _globals.GetColorSchemes().find(schemeName);
+    if (scheme != _globals.GetColorSchemes().end())
+    {
+        return &scheme->second;
+    }
+    else
+    {
+        return nullptr;
+    }
+}

src/cascadia/TerminalApp/CascadiaSettings.h

@@ -70,6 +70,7 @@ public:
     static std::filesystem::path GetDefaultSettingsPath();
 
     const Profile* FindProfile(GUID profileGuid) const noexcept;
+    const ColorScheme* GetColorSchemeForProfile(const GUID profileGuid) const;
 
     std::vector<TerminalApp::SettingsLoadWarnings>& GetWarnings();
 

src/cascadia/TerminalApp/Profile.cpp

@@ -551,7 +551,7 @@ void Profile::SetColorScheme(std::optional<std::wstring> schemeName) noexcept
     _schemeName = std::move(schemeName);
 }
 
-std::optional<std::wstring>& Profile::GetSchemeName() noexcept
+const std::optional<std::wstring>& Profile::GetSchemeName() const noexcept
 {
     return _schemeName;
 }

src/cascadia/TerminalApp/Profile.h

@@ -71,7 +71,7 @@ public:
     void SetGuid(GUID guid) noexcept { _guid = guid; }
     void SetFontFace(std::wstring fontFace) noexcept;
     void SetColorScheme(std::optional<std::wstring> schemeName) noexcept;
-    std::optional<std::wstring>& GetSchemeName() noexcept;
+    const std::optional<std::wstring>& GetSchemeName() const noexcept;
     void SetTabTitle(std::wstring tabTitle) noexcept;
     void SetSuppressApplicationTitle(bool suppressApplicationTitle) noexcept;
     void SetAcrylicOpacity(double opacity) noexcept;

src/cascadia/TerminalApp/TerminalPage.cpp

@@ -554,6 +554,13 @@ namespace winrt::TerminalApp::implementation
         const bool usedManualProfile = (newTerminalArgs != nullptr) &&
                                        (newTerminalArgs.ProfileIndex() != nullptr ||
                                         newTerminalArgs.Profile().empty());
+
+        // Lookup the name of the color scheme used by this profile.
+        const auto* scheme = _settings->GetColorSchemeForProfile(profileGuid);
+        // If they explicitly specified `null` as the scheme (indicating _no_ scheme), log
+        // that as the empty string.
+        const auto schemeName = scheme ? scheme->GetName() : L"\0";
+
         TraceLoggingWrite(
             g_hTerminalAppProvider, // handle to TerminalApp tracelogging provider
             "TabInformation",
@@ -565,6 +572,7 @@ namespace winrt::TerminalApp::implementation
             TraceLoggingBool(settings.UseAcrylic(), "UseAcrylic", "The acrylic preference from the settings"),
             TraceLoggingFloat64(settings.TintOpacity(), "TintOpacity", "Opacity preference from the settings"),
             TraceLoggingWideString(settings.FontFace().c_str(), "FontFace", "Font face chosen in the settings"),
+            TraceLoggingWideString(schemeName.data(), "SchemeName", "Color scheme set in the settings"),
             TraceLoggingKeyword(MICROSOFT_KEYWORD_MEASURES),
             TelemetryPrivacyDataTag(PDT_ProductAndServicePerformance));
     }