[2.5] Fixed the FOBS lazy loading issue

[nvidianz]

Description

FOBS class loader didn't handle lazy-loaded class correctly. So some class can't be found.
It's fixed by using importlib.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Quick tests passed locally by running ./runtest.sh.
• In-line docstrings updated.
• Documentation updated.

[nvidianz]

/build