ui: add the ability to apply `defaultrc` configs from resources We will want the ability to cat out these resources, but the same would apply to templates, so I'm going to wait for the dust to settle on that. Reading the default config directly from the filesystem is still in place for now. Differential Revision: https://phab.mercurial-scm.org/D7776

ui: refactor `readconfig()` into a form that can consume resources The old form can't completely go away, because files outside of packages still need to be read. The name passed in here is a tuple of `package name, resource` as needed by the resource API. I like the idea of stating the config file is embedded in the executable by listing is as `exe!package.resource`. This would be consistent with how `debuginstall` points to the executable for the python executable, lib, and installed modules. While in practice the filesystem path is available from the backing ResourceReader when the resource is opened, it is a relative path on py2 and absolute on py3. Further, while this would show in the `hg config` output for each option if set as such here, it doesn't show in the `reading from...` line when `--debug` is used. The file isn't actually open where that prints, so there's no way I see to get that info there. So I opted for the simple prefix to distinguish resources from files. Differential Revision: https://phab.mercurial-scm.org/D7775

resourceutil: implement `contents()` to iterate over resources in a package Differential Revision: https://phab.mercurial-scm.org/D7774

resourceutil: implement `is_resource()` This will be needed when iterating resources. Differential Revision: https://phab.mercurial-scm.org/D7773

resourceutil: don't limit resources to the `mercurial` package This should make things a little clearer, in that it now requires the full package name to access a resource. But the real motivation is that `extensions._disabledpaths()` walks the `hgext` directory looking for bundled extensions. This in turn feeds, among other things: 1) Listing disabled extensions in `hg help extensions` 2) Indicating that an unknown command is in a non-enabled extension 3) Displaying help for non-enabled extensions 4) Generating documentation 5) Announcing LFS is auto-enabled (or not) when cloning from an LFS source The filesystem based ResourceReader will happily return *.py and *.pyc, but the one supplied by PyOxidizer doesn't. Presumably we can change that. The only other idea I had here is for setup.py to generate a text file containing the list of extensions, but that doesn't seem great when running from source. Differential Revision: https://phab.mercurial-scm.org/D7772

setup: include `defaultrc` in the package list This is needed to access the config files via the resourceutil framework, which is needed to embed the config files when uing PyOxidizer. Differential Revision: https://phab.mercurial-scm.org/D7771