bigquery: parse EXECUTE IMMEDIATE in FOR...IN statements

[RedZapdos123]

Summary

• parse BigQuery EXECUTE IMMEDIATE statements in procedural contexts instead of falling back to incomplete command parsing
• support optional INTO and USING clause consumption for EXECUTE IMMEDIATE
• add regression coverage for issue BigQuery: FOR...IN loop not supported? #7483 query pattern (FOR ... IN ... DO EXECUTE IMMEDIATE FORMAT(...))

Closes #7483.

Validation

• python -m pytest tests/dialects/test_bigquery.py -q
  • Result: 58 passed in 6.22s
• make test
  • Result: Ran 1179 tests in 57.236s
• make testc
  • Result: Ran 1090 tests in 27.081s
  • Status: OK (skipped=26)
• direct runtime check: issue BigQuery: FOR...IN loop not supported? #7483 query now parses without ParseError

The validation screenshots of the tests run, locally on WSL: