linelog: correct the default value of `annotateresult.lines` This was flagged by pytype once it was tricked into using the standard `attr` package instead of the vendored copy.

phabricator: correct the default value of `phabhunk.corpus` There's only one caller to this constructor (which does provide this argument), and no direct assignments, so there's no runtime bug here. However, when pytype is tricked into using the standard `attr` package instead of the vendored version, it flags this because bytes is passed to the one constructor invocation. Tricking pytype into using the standard package will generate many more type hints, noteably around `@attr.s` decorated things.

rust-changelog: accessing the index The `Index` object is currently the one providing all DAG related algorithms, starting with simple ancestors iteration up to more advanced ones (ranges, common ancestors…). From pure Rust code, there was no way to access the changelog index for a given `Repository`, probably because `rhg` does not use any such algorithm yet.

typing: add type hints to `mercurial.policy` Mostly trivial, but this seems like the logical module to use to inject the hints from `cext`, `pure`, etc, given that this file has the fallback policy. This is a first step. There doesn't appear to be a predefined type for a module in py3.7, so those are omitted for now.