exchangev2: recognize narrow patterns when pulling pulloperation instances were recently taught to record file include and exclude patterns to facilitate narrow file transfer. Teaching the exchangev2 code to transfer a subset of files is as simple as constructing a narrow matcher from these patterns and filtering all seen file paths through it. Keep in mind that this change only influences file data: we're still fetching all changeset and manifest data. So, there's still a ton of "partial clone" to implement in exchangev2. On a personal note, I derive gratification that this feature requires very few lines of new code to implement. To test this, we implemented a minimal extension which allows us to specify --include/--exclude to clone. While the narrow extension provides these arguments, I explicitly wanted to test this functionality without the narrow extension enabled, as that extension monkeypatches various things and I want to isolate the behavior of core Mercurial. Differential Revision: https://phab.mercurial-scm.org/D5132