Review all TODOs in code

[aclysma]

There are a number of TODOs in the code. Either:

• Remove them if they are no longer relevant
• Fix them
• Or categorize/group them, add issues for them, and reference the issue by ID from the code

[aclysma]

Reviewed and fixed about half of them. The remaining fall into these categories:

• Error handling that is hard to recover from. For example, a bad shader, being unable to find a suitable device, or not finding appropriate device memory.
• Some symbol names I'm not completely happy with
• Sample code I'd like to add to the examples
• Would like to improve how errors are passed to user code. (Currently downstream code calls into a function that never returns.. because this is how winit works)
• More error checking during initialization for extension/layer handling
• Some fields that shouldn't be public in TimeState
• Use a circular buffer in FPS counting
• Some non-critical open questions in handling swap chain frame presents

[aclysma]

Since rustfmt is set up on CI, we could break remaining TODOs into issues and use this option:
report_todo = "Unnumbered"
report_fixme = "Unnumbered"