templatespec: create a factory function for each type there is Most of the arguments to the `templatespec` constructor are mutually exclusive, so each combination creates a different type of templatespec. Let's clarify that by creating factory functions. I've left the callers in `logcmdutil` unchanged for now because they are more complex and `logcmdutil.templatespec()` is slightly higher level in that it is specific to changesets. My larger goal is to add support frozen binaries (specifically PyOxidizer) by adding a specific type of `templatespec` for built-in templates. That will get its own factory function. Differential Revision: https://phab.mercurial-scm.org/D8845

templater: stop accepting a single style to stylemap() The code seems to have been for compatibility across d3dbdca92458 (hgweb: don't choke when an inexistent style is requested (issue1901), 2009-11-12). Differential Revision: https://phab.mercurial-scm.org/D8844

formatter: inline a variable assigned from `templater.templater.frommapfile` The variable doesn't get reused and it doesn't help formatting, so I don't see any reason for it. Differential Revision: https://phab.mercurial-scm.org/D8807