Mechanism for finding out where an error started and context around said error

[resolritter]

From #831 (comment)

I think the biggest downside to using a Tree-sitter parser in a compiler front-end is that, while we've done a lot of work on Tree-sitter's error recovery, we haven't yet built out functionality for error messages. So it isn't trivial to find out the exact token/position where the error initiated, and get a list of expected tokens, and things like that.

The proposed use-case in the linked discussion is being able to use the generated parser in the compiler front-end for a language. That being the scenario, continuing after the error is not necessary since code emission could stop at the first syntax error found.

What needs to be done

• "Stop-at-first-error" mode
• Error Context
  • The line and column where it started
  • List of constructs which are supposed to be in the error's position (semantic error)
  • List of tokens which were missing or were misplaced (grammatical error)

[razzeee]

This has some intersection with #255