Run custom connection form validators

[bobu-putheeckal]

What

Run legacy provider connection form validators for submitted extra fields when connections are created or updated through the API-backed UI form. This restores custom get_connection_form_widgets() validator callbacks returning validation errors instead of saving invalid values.

Fixes #64835

Tests

• PYTHONPATH="airflow-core/src:devel-common/src:shared/configuration/src:shared/dagnode/src:shared/listeners/src:shared/logging/src:shared/module_loading/src:shared/observability/src:shared/plugins_manager/src:shared/providers_discovery/src:shared/secrets_backend/src:shared/secrets_masker/src:shared/serialization/src:shared/state/src:shared/template_rendering/src:shared/timezones/src:task-sdk/src" uv run --project airflow-core --no-sync pytest airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py -k "form_widget_validator"
• PYTHONPATH="airflow-core/src:devel-common/src:shared/configuration/src:shared/dagnode/src:shared/listeners/src:shared/logging/src:shared/module_loading/src:shared/observability/src:shared/plugins_manager/src:shared/providers_discovery/src:shared/secrets_backend/src:shared/secrets_masker/src:shared/serialization/src:shared/state/src:shared/template_rendering/src:shared/timezones/src:task-sdk/src" uv run --project airflow-core --no-sync ruff check airflow-core/src/airflow/api_fastapi/core_api/services/public/connections.py airflow-core/src/airflow/api_fastapi/core_api/routes/public/connections.py airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py
• PYTHONPATH="airflow-core/src:devel-common/src:shared/configuration/src:shared/dagnode/src:shared/listeners/src:shared/logging/src:shared/module_loading/src:shared/observability/src:shared/plugins_manager/src:shared/providers_discovery/src:shared/secrets_backend/src:shared/secrets_masker/src:shared/serialization/src:shared/state/src:shared/template_rendering/src:shared/timezones/src:task-sdk/src" uv run --project airflow-core --no-sync ruff format --check airflow-core/src/airflow/api_fastapi/core_api/services/public/connections.py airflow-core/src/airflow/api_fastapi/core_api/routes/public/connections.py airflow-core/tests/unit/api_fastapi/core_api/routes/public/test_connections.py

Notes

No frontend files were changed, so frontend tests, eslint, and tsc were not run. A broader initial uv run pytest ... from the workspace root was blocked by jpype1 requiring a Java runtime for the all-extras JDBC dependency on this machine.

[kaxil]

PR template hasn't been followed on any of your PRs. As such I am closing all your PRs since I see little to no evidence of actual testing and mass PRs to Airflow & other repos.