SNOW-1873529: Add support for empty semi-structured StructType and ArrayType to ast

[sfc-gh-jrose]

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

   Fixes SNOW-1873529

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
     • If this test skips Local Testing mode, I'm requesting review from @snowflakedb/local-testing
   • I am adding new logging messages
   • I am adding a new telemetry message
   • I am adding new credentials
   • I am adding a new dependency
   • If this is a new feature/behavior, I'm adding the Local Testing parity changes.
   • I acknowledge that I have ensured my changes to be thread-safe. Follow the link for more information: Thread-safe Developer Guidelines

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

This change adds support for ArrayType and StructType having empty elements/fields in the AST. An ArrayType without an element_type represents a semi-structured Array. A StructType with fields set to None represents a semi-structured OBJECT. This semantics change is gated behind a client-side parameter in snowflake.snowpark.context.

With the new semantics enabled, OBJECTS are handled differently now. Previously semi-structred objects were represented with MapType(StringType(), StringType()) while structured objects were represented with StructType([...]). After this change both are represented with StructType and MapType only represents MAP columns.