honour XrWeaveSubmitMonoIn2DDXR in comp_d3d11_service weave_submit for present-owners (Windows browser menus over woven content) #1798

Follow-up to #1796 / #1797. XR_DXR_weave v13 XrWeaveSubmitMonoIn2DDXR is honoured only by the desktop-Linux weave engine. Every other service accepts it and ignores it, so the output stays woven.

Ask: honour XrWeaveSubmitMonoIn2DDXR in comp_d3d11_service_weave_submit for present-owners. The motivating case is Windows browser menus over woven content. While the session's hardware state is 2D as confirmed by the DP, the service should skip process_atlas and present the flat view, using the same view rule as the Linux engine (u_weave_flat_view_index):

• stereo: view 0, the left half of each batch rect, unsqueezed;
• N > 2: the view nearest the display axis.

The wire already carries ipc_arg_weave_submit::mono_in_2d. The D3D11 branch of ipc_handle_weave_submit currently drops it.

Things to settle on Windows:

• Hardware-state latching. "Confirmed 2D" is hw_override == 0 plus the DP's acceptance (dp_request_display_mode_confirmed). It must not be the wish-mask state.
• The forced-3D path. It should not fight the hold: weave_force_3d_if_needed already stands down on hw_override == 0.
• Browser side. Windows popups (0069) use flat regions, not a hardware hold, so the browser needs its own Windows trigger before this is user-visible.

Reference implementation: comp_multi_weave_linux.c weave_run_frame (the mono band) and the headless weave_present_vk_linux --test-hold-flicker.