Implement append and split_off for BitVec (RFC 509)

[jooert]

cc #19986

r? @gankro

[Gankra]

I'd appreciate a more useful name than b.

[Gankra]

Sorry for the delayed response. Review done!

[jooert]

Thank you for your review! I fixed everything you noted, except for the assertion regarding the internal representation and the feature gate.

[Gankra]

Alright, r=me with the feature gate fixed (which I'll go ping someone to get an answer on).

[jooert]

I have changed the name of the feature gate to bit_vec_append_split_off. So everything should be fine now.

[alexcrichton]

I think the feature list in this documentation (and the above example) will need to be updated. You can also be sure to run these tests with make check-stage2-doc-crate-collections

[jooert]

@alexcrichton Fixed everything you noted and had to update the call to Vec::drain since it takes a range parameter now.

[alexcrichton]

@bors: r=Gankro 9fa6e4c

Thanks @jooert!

[bors]

⌛ Testing commit 9fa6e4c with merge 3d544f2...