Resolve UUID strings when matching players

[Jikoo]

Allows commands such as /trust to target arbitrary UUIDs. Not a frequent thing, but improves mod support without requiring an addon. Addon would still be better UX, i.e. /modtrust build create or similar instead of /trust <uuid of Create fake player>, but it would at least allow GP to function to some degree for advanced users. Servers could also set up a /trustmodname in their commands.yml:

aliases:
  trustmodname:
  - "trust <mod fake player UUID>"

Also allows targeting offline players via commands more reliably, i.e. a player data cleanup system might run commands from several plugins during an inactivity purge. /deleteallclaims John_Minecraft fails if John_Minecraft has not logged in since server restart, but /deleteallclaims <John_Minecraft's uuid> would succeed after this PR.
The only current case where UUID targeting is allowed is /adjustbonusclaimblocks

The only command blocked from arbitrary UUID execution is /givepet because it would allow users to give pets to nonexistent players, creating a mess that would require admin intervention.

Closes #1305
Closes #1586
/e: also #1970