templater: replace templatepath() with function that also opens the file For frozen binaries, such as those created by PyOxidizer, I plan to make it so the templatespec can keep an opened file/resource to read from instead of needing a file path. Having `templatepath()` return an opened file should help with that. At this point, it's just a wasteful extra opening of mapfiles that we'll open again later. I'll update the read-side next so it reads from the file-like object without opening the file again. Differential Revision: https://phab.mercurial-scm.org/D8892

templater: start passing resource to read from into _readmapfile() This patch makes it so we pass in a file-like resource to read from instead of having `_readmapfile()` open the file. This is one more step towards making `_readmapfile()` able to read resources opened by from `importlib.resources`. We still need to pass in the mapfile path because it's used for loading dependent mapfiles from `%include` and `__base__`, and it's also used for giving the user better error messages. Besides that, one can safely call `_readmapfile()` with any file-like resource after this patch. Differential Revision: https://phab.mercurial-scm.org/D8891

templater: move stylemap() to hgweb_mod, since that's its only user `stylemap()` even has an error message that mentions "hgweb templates", so it seems that it's meant specifically for hgweb. Differential Revision: https://phab.mercurial-scm.org/D8890