refactor version checks for pandas, pyarrow

[tswast]

We're using pkg_resources.parse_version from setuptools, which is just a thin wrapper over packaging.

• parse_version implementation: https://github.com/pypa/setuptools/blob/a4dbe3457d89cf67ee3aa571fdb149e6eb544e88/pkg_resources/__init__.py#L112
• Our usage: https://github.com/googleapis/python-bigquery/search?q=pkg_resources

Also, we have some version comparisons for features. I think it'd be cleaner to implement these as properties like we do in BQStorageVersions that I propose adding in #748

import packaging.version


_MIN_BQ_STORAGE_VERSION = packaging.version.Version("2.0.0")
_BQ_STORAGE_OPTIONAL_READ_SESSION_VERSION = packaging.version.Version("2.6.0")


class BQStorageVersions:
 def __init__(self):
 self._installed_version = None

 @property
 def installed_version(
 self,
 ) -> Union[packaging.version.LegacyVersion, packaging.version.Version]:
 if self._installed_version is None:
 from google.cloud import bigquery_storage

 self._installed_version = packaging.version.parse(
 getattr(bigquery_storage, "__version__", "legacy")
 )

 return self._installed_version

 @property
 def is_read_session_optional(self) -> bool:
 return self.installed_version >= _BQ_STORAGE_OPTIONAL_READ_SESSION_VERSION

 def verify_version(self):
 """Verify that a recent enough version of BigQuery Storage extra is installed.

 The function assumes that google-cloud-bigquery-storage extra is installed, and
 should thus be used in places where this assumption holds.

 Because `pip` can install an outdated version of this extra despite the constraints
 in setup.py, the the calling code can use this helper to verify the version
 compatibility at runtime.

 Raises:
 LegacyBigQueryStorageError: If google-cloud-bigquery-storage is outdated.
 """
 if self.installed_version < _MIN_BQ_STORAGE_VERSION:
 msg = (
 "Dependency google-cloud-bigquery-storage is outdated, please upgrade "
 f"it to version >= 2.0.0 (version found: {self.installed_version})."
 )
 raise LegacyBigQueryStorageError(msg)


BQ_STORAGE_VERSIONS = BQStorageVersions()

[plamut]

I support this.

As a bonus, this will make it easier to break the dependency on setuptools if we choose to switch to a different build system at some point.

[tswast]

We don't have any version checks for google-cloud-core as of #1487