Add support for DECFLOAT type

[sfc-gh-bkogan]

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

   Fixes SNOW-2185194

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 adds support for the DECFLOAT numeric data type, which is a decimal floating-point number. decimal.Decimal literals are still inferred as NUMBER type. Not sure if we can change that in any way without being backwards incompatible. Users can use lit with an explicit datatype argument for now.

   From reading the connector PR, it seems that the user is expected to set the decimal context to precision 38 in order to preserve the precision stored on the server. I kept that behavior here.

[sfc-gh-yuwang]

Hi @sfc-gh-heshah , can you help review the IR part of this PR? Thank you!

[sfc-gh-heshah]

LGTM from AST perspective, thanks @sfc-gh-bkogan!