[mlir][OpenMP] - Transform target offloading directives with dependencies during PFT to MLIR conversion

This patch changes PFT to MLIR lowering for the following directives
when they have the `depend` clause on them.

!$ omp target depend(..)
!$ omp target enter data depend(..)
!$ omp target update data depend(..)
!$ omp target exit data depend(..)

Lowering now involves the creation of an `omp.task` operation that encloses
the `omp.target` operation that is otherwise generated for the target construct.
In addition, the depend clause from the target is moved to the enclosing
new `omp.task`. The new `omp.task` is a mergeable task.

```
!$ omp target map(..) depend(in:a)
   b = a
```
is transformed to the following MLIR

```
omp.task mergeable depend(in:a) {
  omp.target map(..) {
    //MLIR for b = a;
  }
  omp.terminator
}
```

Author: bhandarkar-pranav

flang/lib/Lower/OpenMP/ClauseProcessor.cpp

@@ -817,6 +817,7 @@ bool ClauseProcessor::processTargetDepend(
   firOpBuilder.setInsertionPointToStart(&taskOp.getRegion().front());
   return true;
 }
+
 bool ClauseProcessor::processIf(
     omp::clause::If::DirectiveNameModifier directiveName,
     mlir::omp::IfClauseOps &result) const {