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