Replace mcfunction grammar

[RitikShah]

I'm replacing the grammar for mcfunction (introduced in #4425 by @Arcensoth) from language-mcfunction to syntax-mcfunction.

Description

syntax-mcfunction is a new grammar written from scratch to support the newer features of Minecraft commands in newer versions of the game. This grammar was actually a prototype of a rework that Arcensoth and I planned on working together on. Unfortuntely, Arcensoth unexpectedly passed away. This grammar is now in the MinecraftCommands org so that it's easier to get more contributors from the community (atm, I'm the sole maintainer).

The README contains a lot of detail for how this grammar differentiates itself from the original but the key differences are that it supports multi-line command and it lacks a lot of error highlighting to support future versions and custom commands (via mods or custom pre-processors). This is much more of a permissive highlighter which supports more of the community projects (such as bolt which can specify .bolt files being highlighted by the .mcfunction language via a .gitattributes file).

Checklist:

• I am changing the source of a syntax highlighting grammar
  • Old: https://github.com/Arcensoth/language-mcfunction
  • New: https://github.com/MinecraftCommands/syntax-mcfunction

Questions

It seems like I have 1 warning related to the say repo, I'm not entirely sure how to parse this so I might need some help to figure this out. Please let me know if I need to follow any other instructions from the contributing guide.

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.