Refactor in SyntaxDefinition and related classes.

Minor improvements in CPP, CSS, xit syntax highlighting.
AI Assistant / LLM Chat now can restore previous opened chats and states (last model used, panel split), can have private conversations, can clone a previous conversation, plus some visual improvements.
Fixed a bug in tab widget splitting.

src/tools/ecode/plugins/aiassistant/aiassistantplugin.hpp

@@ -38,6 +38,8 @@ class AIAssistantPlugin : public PluginBase {
 
 	LLMChatUI* newAIAssistant();
 
+	void onSaveState( IniFile* state ) override;
+
   protected:
 	LLMProviders mProviders;
 	bool mUIInit{ false };