Add ECR::Lexer::SyntaxException with location info

[nobodywasishere]

Closes #15220. Don't know if I should add a rescue to ECR.process_string that re-raises as a ECR::SyntaxException, for now though I think this works. Didn't end up going with Crystal::SyntaxException as that required pulling in the entire ast / parser / compiler files which seemed silly for a simple exception.

[Sija]

Would be great to have this reviewed and released as a part of Crystal 1.15.0

[straight-shoota]

suggestion: To simplify the implementation, we could introduce a custom raise method which raises the appropriate SyntaxException at the current location:

privat def raise(message)
  ::raise SyntaxException.new(message, @line_number, @column_number)
end

The existing calls like raise "Unexpected end of file inside <%= ..." would stay as they are, but now they'd target the instance method instead of the global ::raise.

[nobodywasishere]

@straight-shoota I would prefer naming it something like syntax_error instead of overwriting a common top-level method personally, as it could lead to confusion. I can switch to a common method for raising syntax exceptions though.

[straight-shoota]

We use instance methods to shadow ::raise in other places in the compiler as well, so it wouldn't be unprecedented.

But I'm fine either way.

[Sija]

Any chances to include this into v1.15.0?