Rewrite regex for project names to be not prone to catastrophic backtracking

Summary: Fixes T15371

Test Plan:

• Save the text {{#translation:}} in remarkup and see that it renders.
• Create a project or projects with the hashtags a, b, ab, foo, f.o.o.
• Observe that both before and after this patch you can link to all of them by hashtag.
• Create a project or projects with the hashtags a., .b, .foo, foo..
• Observe that both before and after this patch you can link to none of them by hashtag.

Reviewers: O1 Blessed Committers, aklapper

Reviewed By: O1 Blessed Committers, aklapper

Subscribers: aklapper, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15371

Differential Revision: https://we.phorge.it/D25838