Update Dear ImGui to 1.92.9b (docking)

From 947aa9c97 to 98a66d8c8 on the docking branch - the latest release there,
plus the viewport fixes that landed on top of it. The only local changes to
upstream files are the "#undef new" hack at the top of imgui.h and enabling
IMGUI_DISABLE_OBSOLETE_FUNCTIONS in imconfig.h; both re-applied.

1.92 reworked fonts and textures, so the thin3d backend now advertises
ImGuiBackendFlags_RendererHasTextures and creates/updates/destroys imgui's
textures on request instead of building the font atlas itself. ImTextureIDs
below 256 now index those, above it the per-frame temp textures as before.
thin3d can't replace part of a texture yet, so an update re-uploads the whole
thing - fine for an atlas that only changes when a new glyph appears.

Also: AddRect() swapped its thickness and flags parameters in 1.92.8.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

UI/NativeApp.cpp

@@ -375,8 +375,8 @@ void runImDebugger(Draw::DrawContext *draw) {
 				{node->Pos.x + node->Size.x, node->Pos.y + node->Size.y},
 				IM_COL32(255, 255, 255, 90),
 				0.f,
-				ImDrawFlags_None,
-				1.f
+				1.f,
+				ImDrawFlags_None
 			);
 		}
 		imDebugger_->Frame(currentDebugMIPS, gpu, draw);