This commit add an NVIDIA-specific lowering of `cf.assert` to to
`__assertfail`.

Note: `getUniqueFormatGlobalName`, `getOrCreateFormatStringConstant` and
`getOrDefineFunction` are moved to `GPUOpsLowering.h`, so that they can
be reused.

Adds initial support for lowering the `loop` directive to MLIR.

The PR includes basic suport and testing for the following clauses:
 * `collapse`
 * `order`
 * `private`
 * `reduction`

Parent PR: #113911, only the latest commit is relevant to this PR.

This patch implements the `ConvertToLLVMPatternInterface` for the OpenMP
dialect, allowing `convert-to-llvm` to act on the OpenMP dialect.

This commit marks the type converter in `populate...` functions as
`const`. This is useful for debugging.

Patterns already take a `const` type converter. However, some
`populate...` functions do not only add new patterns, but also add
additional type conversion rules. That makes it difficult to find the
place where a type conversion was added in the code base. With this
change, all `populate...` functions that only populate pattern now have
a `const` type converter. Programmers can then conclude from the
function signature that these functions do not register any new type
conversion rules.

Also some minor cleanups around the 1:N dialect conversion
infrastructure, which did not always pass the type converter as a
`const` object internally.

This patch adds conversion patterns to LLVM for the following OpenMP
dialect operations:
  - `omp.critical.declare`
  - `omp.cancel`
  - `omp.cancellation_point`
  - `omp.distribute`
  - `omp.teams`
  - `omp.ordered`
  - `omp.taskloop`

Also, arbitrary sorting of operations when passing them as template
argument lists when configuring that pass is replaced by alphabetical
sorting.

This operation did not model the behaviour of reductions in the openmp
standard. It has since been replaced by block arguments on the outer
operation. See https://github.com/llvm/llvm-project/pull/79308 and
https://github.com/llvm/llvm-project/pull/80019

This patch updates the definition of `omp.simdloop` to enforce the
restrictions of a wrapper operation. It has been renamed to `omp.simd`,
to better reflect the naming used in the spec. All uses of "simdloop" in
function names have been updated accordingly.

Some changes to Flang lowering and OpenMP to LLVM IR translation are
introduced to prevent the introduction of compilation/test failures. The
eventual long term solution might be different.

This patch proposes the renaming of certain OpenMP dialect operations with the
goal of improving readability and following a uniform naming convention for
MLIR operations and associated classes. In particular, the following operations
are renamed:

- `omp.map_info` -> `omp.map.info`
- `omp.target_update_data` -> `omp.target_update`
- `omp.ordered_region` -> `omp.ordered.region`
- `omp.cancellationpoint` -> `omp.cancellation_point`
- `omp.bounds` -> `omp.map.bounds`
- `omp.reduction.declare` -> `omp.declare_reduction`

Also, the following MLIR operation classes have been renamed:

- `omp::TaskLoopOp` -> `omp::TaskloopOp`
- `omp::TaskGroupOp` -> `omp::TaskgroupOp`
- `omp::DataBoundsOp` -> `omp::MapBoundsOp`
- `omp::DataOp` -> `omp::TargetDataOp`
- `omp::EnterDataOp` -> `omp::TargetEnterDataOp`
- `omp::ExitDataOp` -> `omp::TargetExitDataOp`
- `omp::UpdateDataOp` -> `omp::TargetUpdateOp`
- `omp::ReductionDeclareOp` -> `omp::DeclareReductionOp`
- `omp::WsLoopOp` -> `omp::WsloopOp`

Introduces conversion of `omp.private`'s regions to the LLVM dialect.
This reuses the already existing conversion pattern for
`ReducetionDeclareOp` and repurposes it to be used for multi-region ops
as well.

Adds a new test for offloading `target update` directive to AMD GPUs.