Fix: address staged file path edge case in snowflake parsing

[georgesittas]

The behavior today in main is as follows:

MODEL (
  name test_schema.@{table_name},
  kind FULL,
  blueprints (
    (table_name := "test_table", stage_path := 'foo'),
  )
);

SELECT * FROM @stage_path (file_format => 'bar') LIMIT 100

(.venv) ➜  sqlmesh render test_schema.test_table
Error: Failed to resolve macros for
SELECT
  *
FROM @stage_path(file_format => 'bar')
LIMIT 100
Macro 'stage_path' does not exist. at '.../playground/models/test_model.sql'

This is because the parsing is off:

>>> from sqlmesh.core.dialect import parse_one
>>> parse_one("""
... SELECT
...   *
... FROM @stage_path (FILE_FORMAT => 'foo')
... LIMIT 100
... """, dialect="snowflake")
Select(
  expressions=[
    Star()],
  limit=Limit(
    expression=Literal(this=100, is_string=False)),
  from=From(
    this=Table(
      this=MacroFunc(
        this=Anonymous(
          this=stage_path,
          expressions=[
            Kwarg(
              this=Var(this=FILE_FORMAT),
              expression=Literal(this='foo', is_string=True))])))))

Notice the MacroFunc here. Instead, we want this to be a StagedFilePath, because we can't disambiguate it from Snowflake's stage file syntax.

Alternatively, if I change the variable reference to @{stage_path}, then it fails with "Expecting ). Line 9, Col: 43." (=> highlighted).