[flang] Add semantics tests for lock-stmt

Add three tests for lock-stmt. The first includes
standard-conforming statements, the second includes
non-standard-conforming statements because of errors where
something unexpected occurs, such as a missing lock-variable,
and the third includes non-standard-conforming statements
because of semantic errors, such as type or rank mismatches.

Reviewed By: rouson

Differential Revision: https://reviews.llvm.org/D136628