SNOW-1887104: Update OBJECT semantics

[sfc-gh-jrose]

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

   Fixes SNOW-NNNNNNN

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
   • If adding any arguments to public Snowpark APIs or creating new public Snowpark APIs, I acknowledge that I have ensured my changes include AST support. Follow the link for more information: AST Support Guidelines

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

   This change modifies the semantics for OBJECT type when the _use_structured_type_semantics flag is enabled. In this mode both semi-structured and structured OBJECT data will be represented by StructType and MapType only refers to structured MAP data.

Without the flag semi-structured data will continue to refer to MapType(StringType(), StringType()) while structured OBJECT will refer to StructType.

[sfc-gh-snowflakedb-snyk-sa]

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