evolve: prompt user for branch selection while resolving content-divergence
When resolving content-divergence, there can be case when both the
content-divergent changesets are on different named branches. In that case, we
are not sure which branch should the resolution commit should be on.
This patch adds logic to prompt user to choose the branch which the resolution
commit should be on and then creates the new resolution commit on that branch.
This also adds a new test file which have tests for the branch selection feature
we have added.