Corrections to Snowflake grammar for explicit precedence

[jimidle]

PR #548 unfortunately incorrectly removed support for parenthesized expressions.

This was not caught because we had no coverage tests for expression precedence so an expression such as:

(a + b) * c

Generates a syntax error.

The PR also:

• removed bracketExpression from the expr rule, but left it in the grammar despite being unused (removing it would have pointed out its real use in the IR generator)
• Incorrectly duplicated COLON id

Here we reinstate expression precedence correctly, add test coverage for the grammar changes that were made, and correct the duplication of COLON id

[github-actions[bot]]

Coverage tests results

401 tests  ±0   154 :white_check_mark: ±0   4s :stopwatch: ±0s   2 suites ±0     0 :zzz: ±0    2 files   ±0   247 :x: ±0 

For more details on these failures, see this check.

Results for commit 86e75b33. ± Comparison against base commit 6a998060.

:recycle: This comment has been updated with latest results.