[OpenMP][IRBuilder] Don't initialize `kmp_dep_info` instances in alloc regions (#131795)

Fixes #121289

Given the following MLIR, where a variable: `x`, is `private` for the
`omp.parallel` op and a `depend` for the `omp.task` op:
```mlir
omp.private {type = private} @_QFEx_private_i32 : i32
llvm.func @nested_task_with_deps() {
  %0 = llvm.mlir.constant(1 : i64) : i64
  %1 = llvm.alloca %0 x i32 {bindc_name = "x"} : (i64) -> !llvm.ptr
  omp.parallel private(@_QFEx_private_i32 %1 -> %arg0 : !llvm.ptr) {
    omp.task depend(taskdependout -> %arg0 : !llvm.ptr) {
      omp.terminator
    }
    omp.terminator
  }
  llvm.return
}
```

Before the fix proposed by this PR, the IR builder would emit the
allocation and the initialzation logic for the task's depedency info
struct in the parent function's alloc region:
```llvm
define void @nested_task_with_deps() {
  ....
  %.dep.arr.addr = alloca [1 x %struct.kmp_dep_info], align 8
  %2 = getelementptr inbounds [1 x %struct.kmp_dep_info], ptr %.dep.arr.addr, i64 0, i64 0
  %3 = getelementptr inbounds nuw %struct.kmp_dep_info, ptr %2, i32 0, i32 0
  %4 = ptrtoint ptr %omp.private.alloc to i64
  store i64 %4, ptr %3, align 4
  ....
  br label %entry

omp.par.entry:                                    ; preds = %entry
  ....
  %omp.private.alloc = alloca i32, align 4
```

Note the following:
- The private value `x` is alloced where it should be in the parallel
op's entry region,
- howerver, since the privae value is also a depedency of the task and
since allocation and initialzation of the task depedency info struct
both happen in the alloc region,
- this results in the private value being referenced before it is
actually defined.

This PR fixes the issue by only allocating the task depedency info in
the alloc region while initialzation happens in the current IP of the
function with the rest of the logic that depends on it.