Maintain SQLGlot Fork to make it's optimizer more compatible

[vineetg3]

We need to maintain a forked version of SQLGlot to address incompatibilities between our requirements and the standard SQLGlot optimizer.

We're currently skipping problematic rules:

• The canonicalize rule (12) removes nested DATE functions, causing data loss:

  DATE(DATE(a,b),c) -> DATE(a,b)  # 'c' argument disappears
  

• merge_subqueries rules break ANTI/SEMI joins if not conditionally skipped.
• unnest_subqueries creates tries to remove ANTI/SEMI join but creates aliases with no corresponding tables.

Proposed Solution

Fork SQLGlot to fix these optimizer bugs directly in the source, allowing us to use the optimizer without skipping critical rules.

[knassre-bodo]

The nature of this issue has now changed since some of the skipped passes have been re-added, while others have been augmented via override files.