Improve parsing around mismatched brackets

When brackets are mismatched, it's typical for the parsing of the rest of the file to be broken.

In order to improve the experience with formatting incorrect or incomplete code, we should detect these cases and implicitly terminate the brackets.

The brackets can be implicitly terminated when a semicolon is encountered (unless in a semicolon list: constant record, generic type parameters, function parameters), or when a keyword that can only occur at the start of a line is encountered.