feat: add REPL for plugins (#6120)

This can be enabled by setting the `.plugins.repl.enabled` setting to true


Close Chatterino and make a backup of your settings.json before attempting any modifications.
```json5
{
  "plugins": {
    "repl": {
      "enabled": true,
    },
  },
}
```

src/controllers/plugins/Plugin.hpp

@@ -6,6 +6,7 @@
 #    include "controllers/plugins/LuaUtilities.hpp"
 #    include "controllers/plugins/PluginPermission.hpp"
 
+#    include <boost/signals2/signal.hpp>
 #    include <QDir>
 #    include <QString>
 #    include <QUrl>
@@ -21,6 +22,10 @@
 struct lua_State;
 class QTimer;
 
+namespace chatterino::lua::api {
+enum class LogLevel;
+}  // namespace chatterino::lua::api
+
 namespace chatterino {
 
 struct PluginMeta {
@@ -137,12 +142,20 @@ public:
     bool hasHTTPPermissionFor(const QUrl &url);
     bool hasNetworkPermission() const;
 
+    void log(lua_State *L, lua::api::LogLevel level, QDebug stream,
+             const sol::variadic_args &args);
+
+    sol::state_view state();
+
     std::map<lua::api::EventType, sol::protected_function> callbacks;
 
     // In-flight HTTP Requests
     // This is a lifetime hack to ensure they get deleted with the plugin. This relies on the Plugin getting deleted on reload!
     std::vector<std::shared_ptr<lua::api::HTTPRequest>> httpRequests;
 
+    boost::signals2::signal<void()> onUnloaded;
+    boost::signals2::signal<void(lua::api::LogLevel, const QString &)> onLog;
+
 private:
     QDir loadDirectory_;
     lua_State *state_;