templater: fix reading of templates in frozen binaries with py3 < 3.7
When using a frozen binary with py3 < 3.7, there's no
`importlib.resources` module, so we use the code path that reads the
resources from the file system. That code path expects bytes for
package name and resource name.
Differential Revision: https://phab.mercurial-scm.org/D9008
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}