refactor: replace GetText() calls with AST-based parsing in visitor

Andrew Newdigaterequested to merge
less-text-rendering into main

Improves performance and resilience by eliminating unnecessary string conversions and text comparisons. Changes include:

  • Use union.ALL() token check instead of string contains for UNION ALL
  • Add hasWildcard() helper to check for '*' terminal nodes directly
  • Add extractSimpleVariable() to validate simple variable expressions
  • Add containsAggregateFunction() to recursively detect aggregates via AST
  • Replace visitNotExpr text parsing with ctx.AllNOT() token counting

This reduces reliance on GetText() which performs text rendering of the AST, making the translator more efficient and less error-prone.

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