Fixes #10406 ImGui_ImplOpenGL3_Shutdown() calls imgl3wShutdown() which dlcloses the GL library handles but does not zero out the imgl3w function pointer table (imgl3wProcs). When a GLArea is re-realized (e.g. during reparenting), ImGui_ImplOpenGL3_Init() calls ImGui_ImplOpenGL3_InitLoader() which checks "if (glGetIntegerv == nullptr)". Since the stale pointers are non-null, it skips re-initialization. The next GL call through a dangling function pointer causes a SIGSEGV. Fix this by introducing ImGui_ImplOpenGL3_ShutdownWithLoaderCleanup() which calls the normal shutdown and then zeroes the imgl3wProcs table, forcing the next Init to reload GL function pointers via imgl3wInit(). Also properly destroy the ImGui context and reset widget state in glAreaUnrealize so re-realize starts clean. This was extra but was probably leaking memory.