repl: support syntax highlighting

[redyetidev]

Instead of sending many REPL changes in one PR (#52965), it was recommended to me to implement these one-by-one in several PRs.

First up: Syntax highlighting :tada:

This PR adds RegEx-based syntax highlighting to the REPL.

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Notable change text (if text this short is even worth it): "The REPL now includes syntax highlighting for input."