Updates for mcfunction syntax (lexer/minecraft)

[RitikShah]

In Minecraft 1.20.2, a new grammar feature was added: macros. These allow for lines to start with $ and macro substitutions to be performed within the line via $(<var-name>). They also allow for line-continuations via \.

This issue is here to track these new developments and implement new syntax additions to the pygments lexer (alongside some lingering bugs). We can use the textmate grammar I developed as a comparison.

I fully plan to develop a PR once I get a bit more free time to tackle this but I figured to leave an issue open for this.

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Initial PR (by me): #2107.
Follow Up PR (by @MiemieMethod): #2276