Bitflags in API traces are hard to write and read

[kvark]

Is your feature request related to a problem? Please describe.
When writing a playtest or reading an API trace, it's difficult to reason about bitflag values. See https://github.com/gfx-rs/wgpu/pull/1191/files#diff-78d438d1c2e726454851597e74ab167a9579d6cd83d7f712fcea59173cc2b274R27 for example.

Describe the solution you'd like
Something like https://github.com/kvark/bitflags-serial, where the flags are serialized as VALUE | ANOTHER_VALUE
Another alternative is to turn them into structures like Foo { bit_some: bool, bit_other: bool, ...}, but that's more complicated.

Describe alternatives you've considered
Keep them integers but comment on each use...

Additional context
See upstream in bitflags/bitflags#147
Is also a problem for gfx-rs Warden testing infra.

[cwfitzgerald]

Superseded by #2629