Premising that the constructor of PhutilURI is relatively slow,
because it calls various regular expressions to match the domain, the anchor, etc.
Note that the method PhabricatorEnv::isSelfURI() creates multiple PhutilURI objects,
just to check if a domain is matched.
So, we increase the efficienty of PhabricatorEnv::isSelfURI(), by adding a minimal domains
cache, so to avoid the creation of PhutilURI for each isSelfURI() call.
Note that isSelfURI() can be called multiple ones, especially for big Remarkup documents
with many internal/external links.
Good for your CPU, for your performances, for your environment and for the stress of your
your garbage collector. You're welcome Greta Thunberg.
Closes T16061