[MLGO] Fix InlineAdvisor and ModelUnderTrainingRunner after hasValue removal

Recentlyin 4b6b2487, llvm::Optional's hasValue method was removed as
described in
https://discourse.llvm.org/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor
This breaks InlineAdvisor and ModelUnderTrainingRunner. This patch fixes
them by changing the method to has_value, which hasValue was evaluating
to before.

Differential Revision: https://reviews.llvm.org/D138635