• add compat module

• centralize types and servcies (client) in compat for V1 and V1BETA1
• update all types in google.cloud.aiplatform modules to point to compat.types
• update all services (client) in google.cloud.aiplatform modules to point to compat.services

• In utils.py

• change the WrappedClient to an abstract ClientWithOverride class
• add (Service)ClientWithOverride for each AiPlatformService to predefine _default_version and _version_map
• add a TypeVar AiPlatformServiceClientWithOverride, and update TypeVar AiPlatformServiceClient

• In initializer.py

• add select_version to get_encryption_spec

• In each AiPlatformResourceNoun class

• change client_class to (Service)ClientWithOverride

• In BatchPredictionJob, Endpoint, and Model class

• add client version selection logic

• unit tests

• update existing tests to make sure all tests pass
• add unit tests to make sure AiPlatformServiceClientWithOverride works for V1BETA1 and V1
• point all types and services in tests.unit.aiplatform to V1
• add fixtures to support V1BETA1 tests for explanation related functionality
• make sure all tests pass (merging from fix: add v1 conversion value rule)

Fixes b/180711319 🦕