evolve: store the precursor of phase-divergent in evolvestate This patch makes `hg evolve` store the precursor of phase-divergent changeset in evolvestate so that we don't need to calculate that again.

evolve: move logic to complete interrupted relocation to new fn This moves logic which completed the interrupted relocation to it's own separate function as we will need that function in continuing phase-divergence and content-divergence too.

evolve: move logic to complete interrupted orphan resolution to new fn This patch moves logic which completes an interrupted orphan resolution to it's own new function. We will defining such functions for completing phase-divergence and content-divergence too.

evolve: write data to evolvestate in case on conflicts in phase-divergence This patch makes phase-divergence resolution write data to evolvestate instead of graftstate. The `evolve --continue` handling of phase-divergence is broken which will be done in upcoming patches.

evolve: explicitly turn revs to list before storing into evolvestate The cbor library which we are using cannot handle encoding and decoding Python sets, and revs was set there. Let's convert revs explicitly to list to make sure we don't try writing sets.

tests: add tests of content+parent change creating phase-divergence This patch adds tests which shows handling of phase divergence cases by `hg evolve` command which involved content+parent change. The conflicts case is not handled and will be fixed in upcoming patches.

tests: show first line of commit message in test-evolve-phase-divergence.t This patch adds 'firstline' filter to description in the log template.