Move uses of enum to bitflags! where appropriate #14207
Description
Where an enum has been used to represent C-style flags (which are then |-ed together and represented as some flavor of uint), we should now be using the bitflags! macro, which provides stronger type safety guarantees at no cost.
This gist gives a rough grep of the code base where enums with custom discriminants are being used. Some of these are genuinely enums, while others are being used as flags and should be converted to use bitflags! instead.