Normalize error messages from ANTLR

[TristonianJones]

Feature request checklist

• There are no issues that match the desired change
• The change is large enough it can't be addressed with a simple Pull Request
• If this is a bug, please file a Bug Report.

Change
Currently, when parse errors are detected, the ANTLR error message is passed through from CEL to the caller with some additional formatting to highlight where the error occurs. A recent update to the CEL grammar resulted in a shift in the
error information from ANTLR which has the potential to break upstream tests relying on the exact contents of the original
error from ANTLR.

Example
Introduce a flag-guarded change to normalize error messages from ANTLR in order to ensure that errors can be kept consistent
even in the face of grammar updates.

Alternatives considered
Strip all ANTLR error messages and replace them with a general "invalid syntax" message since the error from ANTLR itself
is not always easy to comprehend.