gui_toolkit 0.22.0

Added

• Synthetic input: platform.inject_event(w, event) queues an event that the next poll_events returns after the system's own, through the same path (hover, focus, shortcuts, text input behave as for a real device). For tests, remote control and macros.
• Reading a frame back without the screen (render/capture.odin): render.capture_request(r, rect) marks the next frame, frame_end copies that frame's render target (or a part of it) into a staging texture just before presenting, and render.capture_poll(r) returns RGBA8 pixels once the GPU is done (it never waits: Pending until then). The picture is what the renderer drew: it works with the window covered, off the screen or hidden, and does not depend on the monitor's scale. Nothing is paid until a capture is asked for. Direct3D 11 (swap chain and offscreen); the wgpu backend answers false.

0.20.0 and 0.21.0 are reserved (feat/canvas-gpu and feat/gpu-accel, not released yet); 0.22.0 follows 0.19.0 on purpose.