context: rename bumped into phasedivergent
Rename bumped context method into phasedivergent and add a deprecation warning
on bumped.
Only update all callers to keep the patch straightforward.
The renaming is done according to
https://www.mercurial-scm.org/wiki/CEDVocabulary.
Differential Revision: https://phab.mercurial-scm.org/D241