Regression in `MAP` literals for `GenericDialect`

[Samyak2]

Summary

MAP { ... } literals are failing with GenericDialect. Example:

SELECT MAP {'a': 1, 'b': NULL}

Fails with:

ParserError("Expected: end of statement, found: {")

This is causing failures in DataFusion tests when trying to upgrade: apache/datafusion#20177

It's a regression from the last release (v0.60.0).