Improve NetImgui integration

[Sixze]

1. Fixed incorrect types used for ports in FImGuiContext::Listen() and FImGuiContext::Connect.
2. Removed bIsRemote as it only causes problems:
   • It prevents ImGui from rendeting, even if we are not connected to the server yet.
   • ImGui remains hidden if the server initiated a disconnection (user clicked the "X" button on the client tab in the server window).
3. Added a check for the ImGuiConfigFlags_ViewportsEnable flag before calling ImGui::UpdatePlatformWindows(), which fixes an ensure after disconnecting from the server.
4. Removed Context.Reset(); from FImGuiModule::FindOrCreateSessionContext(), as it makes ImGui unusable if it fails to connect to the server.