Debugger: Paddle back on multiple inheritance for settings

This is fairly close to the new "standard" pattern for an
individual page but still allows flat access using the same
'settings().' stanza.

Change-Id: I1edbbd64a857a3d3936fb2c21fdc7e3c8ae7a44c
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/debugger/gdb/gdbsettings.cpp

@@ -3,6 +3,8 @@
 
 #include "gdbsettings.h"
 
+#include <coreplugin/dialogs/ioptionspage.h>
+
 #include <debugger/commonoptionspage.h>
 #include <debugger/debuggeractions.h>
 #include <debugger/debuggerconstants.h>
@@ -18,11 +20,15 @@ using namespace Utils;
 
 namespace Debugger::Internal {
 
+GdbSettings &gdbSettings()
+{
+    static GdbSettings settings;
+    return settings;
+}
+
 GdbSettings::GdbSettings()
 {
-    setId("M.Gdb");
-    setDisplayName(Tr::tr("GDB"));
-    setCategory(Constants::DEBUGGER_SETTINGS_CATEGORY);
+    setAutoApply(false);
     setSettingsGroup("DebugMode");
 
     useMessageBoxForSignals.setSettingsKey("UseMessageBoxForSignals");
@@ -250,4 +256,20 @@ GdbSettings::GdbSettings()
     readSettings();
 }
 
+// GdbSettingsPage
+
+class GdbSettingsPage final : public Core::IOptionsPage
+{
+public:
+    GdbSettingsPage()
+    {
+        setId("M.Gdb");
+        setDisplayName(Tr::tr("GDB"));
+        setCategory(Constants::DEBUGGER_SETTINGS_CATEGORY);
+        setSettingsProvider([] { return &gdbSettings(); });
+    }
+};
+
+const GdbSettingsPage settingsPage;
+
 } // Debugger::Internal