Copy repository URI normalization code from Phabricator to Arcanist

Summary: Ref T13546. Move toward smarter remote repository lookup by providing URI normalization code in Arcanist. This diff duplicates code from Phabricator; the next change will collapse it.

Test Plan: Ran unit tests.

Maniphest Tasks: T13546

Differential Revision: https://secure.phabricator.com/D21372