Auto merge of #124952 - compiler-errors:no-error, r=lcnr

Rename some `FulfillmentErrorCode`/`ObligationCauseCode` variants to be less redundant

1. Rename some `FulfillmentErrorCode` variants.
2. Always use `ObligationCauseCode::` to prefix a code, rather than using a glob import and naming them through `traits::`.
3. Rename some `ObligationCauseCode` variants -- I wasn't particularly thorough with thinking of a new names for these, so could workshop them if necessary.
4. Misc stuff from renaming.

r? lcnr

Author: bors