Chat QoL: Tab completions

[RedFlames]

Update:
If #46 gets merged, this becomes Client-side only, currently you can compare the changes here:
https://github.com/RedFlames/CelesteNet/compare/chat-qol-server-only-new..chat-qol-improvements?diff=unified

Plus there's #47 and #48 splitting off different parts of this, leaving only the Tab Completion (client-side) to be merged here, afterwards.

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I'm pretty happy with where this feature branch of mine is at as it stands, so I'll make another PR. I know I still have two other ones that await merging, and this one is a bit heavier too...

Overview:

• chat can be scrolled with PgUp/PgDown, it shows interactive button prompts above the chat
• The server now has some basic info about:
  • what sort of first argument a command expects
  • which commands are aliased to which
  • the auth tags required and it'll be smart about sending the list (regular players won't get /kick as a completion option)
• ... and it can send this info to the client. If the client can handle this new DataType (i.e. the client in this branch) it'll use the info to generate a list of completions for:
  • command names at the initial / at the start of the input or after /help ...
  • player names if a command expects this (e.g. after /tp ...)
  • channel names for /join aka /channel
  • Tab completion only lists "full" command names and if a shorter alias matches it makes sure to list the long version too
  • When accepting a completion, a matching alias will be used to keep the input prompt concise (e.g. type /gc or /globa... -> suggests only /globalchat -> pressing Tab turns either one into /gc )
• Chat and Player List can now be scaled with independent UI Scale in settings