render func.sysdate as SYSDATE()

[sjhewitt]

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1. What GitHub issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes SNOW-589556: sqlalchemy.func.sysdate() does not render parentheses #289 / SNOW-589556

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
   • I am adding new logging messages
   • I am adding new credentials
   • I am adding a new dependency

3. Please describe how your code solves the related issue.

   This adds the visit_sysdate_func method to the SnowflakeCompiler to handle func.sysdate() elements