### Body

We had an issue where extra link class (`AIPlatformConsoleLink`) was removed in [PR](https://github.com/apache/airflow/pull/26836) without removing the class from the `provider.yaml` extra links this resulted in web server exception as shown in https://github.com/apache/airflow/pull/28449


**The Task:**
Add validation that classes of extra-links in provider.yaml are importable

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
DOCS_DIR = ROOT_DIR.joinpath("docs")
PROVIDER_DATA_SCHEMA_PATH = ROOT_DIR.joinpath("airflow", "provider.yaml.schema.json")
PROVIDER_ISSUE_TEMPLATE_PATH = ROOT_DIR.joinpath(
    ".github", "ISSUE_TEMPLATE", "airflow_providers_bug_report.yml"
)
CORE_INTEGRATIONS = ["SQL", "Local"]
errors = []
def _filepath_to_module(filepath: pathlib.Path) -> str:
    p = filepath.resolve().relative_to(ROOT_DIR).as_posix()
    if p.endswith(".py"):
        p = p[:-3]
    return p.replace("/", ".")
def _load_schema() -> dict[str, Any]:
    with PROVIDER_DATA_SCHEMA_PATH.open() as schema_file:
        content = json.load(schema_file)
    return content
def _load_package_data(package_paths: Iterable[str]):
    schema = _load_schema()
    result = {}
    for provider_yaml_path in package_paths:
        with open(provider_yaml_path) as yaml_file:
            provider = yaml.load(yaml_file, SafeLoader)
        rel_path = pathlib.Path(provider_yaml_path).relative_to(ROOT_DIR).as_posix()
        try:
            jsonschema.validate(provider, schema=schema)
        except jsonschema.ValidationError:
            raise Exception(f"Unable to parse: {rel_path}.")
        result[rel_path] = provider
    return result
def get_all_integration_names(yaml_files) -> list[str]: