Fix wgpu dpi scaling

[hazeycode]

Let the upstream Dear imgui backends do the DPI scaling and delete our mouse position hacks.

• Updates glfw backend to imgui 1.91.8-docking (removes mouse pos hacks)
• Hack around Dawn/Vulkan bug viewport extents bug (Vulkan validation layer errors related to window extents gfx-rs/wgpu#1958)
• Fixes DPI scaling for glfw_wgpu backend
• Remove some superfluous downstream hacks

This fixes DPI scaling for glfw_wgpu backend (#3) but exposes a bug in Dawn's vulkan backend. We work around this by ensuring the viewport size is clamped. However, there remains a validation error that results in a crash if the window size is increased; this appears to be a bug in the imgui wgpu backend, where the render target is not resized before the viewport is set.

error: [zgpu] Validation: Viewport bounds (x: 0.000000, y: 0.000000, width: 1927.000000, height: 1206.000000) are not contained in the render target dimensions (1920 x 1200).
 - While encoding [RenderPassEncoder].SetViewport(0.000000, 0.000000, 1927.000000, 1206.000000, 0.000000, 1.000000).

This ought to be fixed or worked-around before this is merged.

Note: We're going to have to bring Dawn up to a newer version at some point but it's no small feat.

To test these changes, check out zig-gamedev/zig-gamedev#755 and run zig build triangle_wgpu-run.

[Copilot]

Pull Request Overview

This pull request fixes DPI scaling issues in the glfw_wgpu backend while also working around a Dawn/Vulkan viewport bug. Key changes include updating the viewport clamping in the wgpu backend, removing redundant mouse position hacks, and adjusting DPI scaling handling in the GLFW implementation.

Reviewed Changes

Copilot reviewed 4 out of 6 changed files in this pull request and generated 2 comments.

File	Description
libs/imgui/backends/imgui_impl_wgpu.h	Removed superfluous macros and wrapped declarations in extern "C".
libs/imgui/backends/imgui_impl_wgpu.cpp	Updated viewport calculation with integer clamping as a workaround for Dawn/Vulkan bug.
libs/imgui/backends/imgui_impl_glfw.h	Added extern "C" block and updated comments regarding known issues.
libs/imgui/backends/imgui_impl_glfw.cpp	Removed DPI scaling multiplications from mouse event callbacks and mouse data updates.

Files not reviewed (2)

• build.zig: Language not supported
• src/backend_glfw_wgpu.zig: Language not supported