SNOW-1491199 Introduce ast.proto to the Snowpark client (#2549)

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

   Fixes SNOW-1491199

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.
- [x] I acknowledge that I have ensured my changes to be thread-safe.
Follow the link for more information: [Thread-safe Developer
Guidelines](https://docs.google.com/document/d/162d_i4zZ2AfcGRXojj0jByt8EUq-DrSHPPnTa4QvwbA/edit#bookmark=id.e82u4nekq80k)

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

Introduce `ast.proto` under `src/snowflake/snowpark/_internal/proto` and
`ast_pb2.py` under the `generated` subdirectory.
`ast.proto` gets created from the contents of
[Snowpark/ast](https://github.com/snowflakedb/snowflake/tree/snowpark-phase-0/Snowpark/ast),
using `ir-dsl-c`. The chain is AST IR -> `ir-dsl-c` -> `ast.proto` ->
Python `protoc` -> `ast_pb2.py`.
We are merging both `ast.proto` and `ast_pb2.py` because the Snowpark
repository is not fully equipped to generate the Python client stubs at
packaging time. This change is a work in progress and blocked behind IT
tickets for an indeterminate amount of time.
A complete description of the AST model is too large to include here. We
are currently working on an AST IR developer guide, as well.

Co-authored-by: Arthur Zwiegincew <[email protected]>
Co-authored-by: Leonhard Spiegelberg <[email protected]>
Co-authored-by: Hemit Shah <[email protected]>
Co-authored-by: Varnika Budati <[email protected]>
Co-authored-by: Eric Vandenberg <[email protected]>

.pre-commit-config.yaml

@@ -81,6 +81,8 @@ repos:
           - flake8-print
         args:
           - --per-file-ignores=tests/*.py:T201 # prints are allowed in test files
+          # Ignore errors for generated protocol buffer stubs
+          - --exclude=src/snowflake/snowpark/_internal/proto/generated/ast_pb2.py
     # Use mypy for static type checking.
 -   repo: https://github.com/pre-commit/mirrors-mypy
     rev: 'v0.991'