Update `bitflags` to 2.2.1
Splits out the bitflags part of https://github.com/servo/core-foundation-rs/pull/545
@bors-servo r+
:pushpin: Commit 0fb387a has been approved by jdm
:hourglass: Testing commit 0fb387abbdf9a5581ff0a54bc952c168eb628349 with merge 048c24a0baf29f41bb50e003d6d572fbb1feb091...
:broken_heart: Test failed - checks-github
:umbrella: The latest upstream changes (presumably b009c87f2da0038bb474800cd88597843e5dbdae) made this pull request unmergeable. Please resolve the merge conflicts.
This causes semver checks to start failing because fn from_bits_unchecked(...) is no longer exposed on bitflags types.
I have rebaesed this PR, so assuming it passes all CI jobs I'll land it. The only substantive change I have made to the original version is to specify bitflags = "2" for the version instead of the exact version. This should make it slightly more compatible with other projects that use different versions of bitflags.