gitserver: Pass pathspecs to git archive

Created by: chrismwendt

Keegan discovered that the "paths" passed to git archive are actually "pathspecs" with glob-like syntax. Git docs:

https://git-scm.com/docs/gitglossary#Documentation/gitglossary.txt-aiddefpathspecapathspec

This PR:

• Renames Paths to Pathspecs to more accurately reflect that reality
• Adds a nominal type type Pathspec string to help avoid footgunning ourselves
• Prefixes pathspecs with :(literal) where appropriate to prevent * and ? from being interpreted as special characters

CC

• @keegancsmith who discovered it
• @tsenart who worked on lockfile detection
• @mollylogue who has been working on sub-repo perms and git archive recently

Test plan

Ran locally, did search-based code intel on a couple commits to exercise the git archive calls in the symbols service.