Factoring some changes out of
https://github.com/zed-industries/zed/pull/61461:
- On Metal and wgpu, bulk-upload instance buffers at the start of the
frame rather than uploading chunks as we draw them. The depth buffer
patch needs this architecture since all opaque quads in the scene are
painted before anything else. This also lets us get rid of the awkward
retry loop when the GPU buffer is too small for the scene.
- On Windows, use a constant buffer for the instance offset rather than
creating SRVs with different `FirstElement`s. `FirstElement` is buggy on
some vendors' drivers, and reusing the SRV object should reduce D3D
runtime overhead.
- Misc. refactoring: remove redundant parameters, deduplicate code,
create fewer bind groups on wgpu, etc.

Fixes https://github.com/zed-industries/zed/issues/49588
Fixes https://github.com/zed-industries/zed/issues/59192

Release Notes:

- Fixed an issue where UI elements would flicker on some Windows
devices.