Update project to work with wgpu 0.19

[sarchar]

Checklist

• [x] cargo clippy reports no issues
• [x] cargo doc reports no issues
• [?] cargo deny issues have been fixed or added to deny.toml
• [x] human-readable change descriptions added to the changelog under the "Unreleased" heading.
  • [x] If the change does not affect the user (or is a process change), preface the change with "Internal:"
  • [x] Add credit to yourself for each change: Added new functionality @githubname.

Description

I've updated the project to work with wgpu-0.19. I don't expect this PR to be merged since it depends on git branches of imgui and imgui-winit-support, but I'm offering it here for anyone else who wants to use the latest wgpu.