Add support for OpenMP is_device_ptr clause for target directives.

Part of #102817.

This patch optimizes `rng::generate_n` for segmented iterators by
forwarding the implementation directly to `std::generate_n`.

- before

```
rng::generate_n(deque<int>)/32          21.7 ns         22.0 ns     32000000
rng::generate_n(deque<int>)/50          30.8 ns         30.7 ns     22400000
rng::generate_n(deque<int>)/1024         492 ns          488 ns      1120000
rng::generate_n(deque<int>)/8192        3938 ns         3924 ns       179200
```

- after

```
rng::generate_n(deque<int>)/32          11.0 ns         11.0 ns     64000000
rng::generate_n(deque<int>)/50          16.2 ns         16.1 ns     40727273
rng::generate_n(deque<int>)/1024         292 ns          286 ns      2240000
rng::generate_n(deque<int>)/8192        2291 ns         2302 ns       298667
```

1. createHvxPrefixPred was computing an invalid byte count for small
predicate types, leading to a crash during instruction selection.
2. HexagonTargetLowering::SplitHvxMemOp assumed the memory vector type
is always simple. This patch adds a guard to avoid processing non-simple
vector types, which can lead to failure.

Patch By:
Fateme Hosseini

Co-authored-by: pavani karveti <quic_pkarveti@quicinc.com>
Co-authored-by: Sergei Larin <slarin@quicinc.com>
Co-authored-by: Pavani Karveti <pkarveti@qti.qualcomm.com>

This ports openxla/stablehlo#2682 implementation by @pearu.

Three tests were added to
`Integration/Dialect/Complex/CPU/correctness.mlir`. I also verified
accuracy using XLA's complex_unary_op_test and its MLIR emitters.

LLVM prints switch cases indented by 2 additional spaces, as follows:
```LLVM
  switch i32 %x, label %default [
    i32 0, label %phi
    i32 1, label %phi
  ]
```

Since this only changes the output IR of update_test_checks.py and does
not change the logic of the File Check Pattern, there seems to be no
need to update the existing test cases.

The test added in #161067 writes artifacts to the current dir, i.e.
`test.o` / `test.dwo` / `test.dwp`, which might not be writeable. Tests
should use `%t` for test artifact location, i.e. `%t.o` / `%t.dwo` /
`%t.dwp` However, since `"test.dwo"` is part of the assembly source file
used as a test input, and that's not something lit will substitute, that
typical approach doesn't work. We can instead ensure the output is in a
good location by running `cd %t` (after setting it up).