tests: fold test-template-filters.t into test-template-functions.t

tests: extract test-template-functions.t from test-command-template.t I decided to not split filters and functions into two test files since we sometimes reimplement a filter as a function.

tests: extract test-template-map.t from test-command-template.t test-command-template.t is one of the slowest tests. Let's split it into 4 files of manageable size.

cleanupnodes: preserve phase of parents of new nodes As Yuya noted in the review of D3818, passing in targetphase=phases.draft would result in advancing the phase boundary of a secret-phase parent. We never pass targetphase=phases.draft so far, but it's a bug waiting to happen. I tried to refactor it so max(parentphase, X) happened in one place, but I couldn't come up with good variables names and I ended up with a "newphase = max(newphase, parentphase)" line, which made the whole block not look any better to me. Differential Revision: https://phab.mercurial-scm.org/D3824

rebase: delete the comment which was not following "do not eat my data" Differential Revision: https://phab.mercurial-scm.org/D3756

tags: unblock log-like template keywords and functions It checks if ctx will be used in template since loading ctx per revision could take extra 10-100msec in total depending on the number of tags.

formatter: provide hint of context keys required by template This allows us to create ctx objects only if necessary. I tried another idea which is to populate ctx from 'repo' and 'node' value on demand. It worked, but seemed unnecessarily complicated. So I chose a simpler one. The datafields argument is a space-separated string for consistency with fm.write() API.

templatefuncs: declare resource requirements for future use

templatefuncs: minimize resource requirements

merge with stable