Fix #1979: Add GETDATE, NOW as aliases and allow CURRENT_TIMESTAMP()

[loubnaB023]

This PR fixes #1979 by extending the parser to recognize additional datetime functions and aliases.

Changes:

1. Updated alasqlparser.jison:

   • Added lexer tokens for NOW, GETDATE, and CURRENT_TIMESTAMP
   • Enhanced PrimitiveValue and FuncValue to support:
     • CURRENT_TIMESTAMP with/without parentheses
     • NOW() and GETDATE() as valid functions

2. Rebuilt the parser

3. Added test/test-now.js to verify parsing of:

   • SELECT NOW()
   • SELECT GETDATE()
   • SELECT CURRENT_TIMESTAMP()
   • SELECT CURRENT_TIMESTAMP
   • SELECT CURRENT_DATE
   • SELECT CURDATE()

[mathiasrw]

Nice. Very nice.

Please rename the test file to test1979.

Please make sure the test file will verify the output of each query that is now supported.