….* to llvm/Frontend/Offloading

This patch moves `clang/tools/clang-linker-wrapper/OffloadWrapper.*` to
`llvm/Frontend/Offloading` allowing them to be reutilized by other projects.

Additionally, it makes minor modifications to the API to make it more flexible.
Concretely:
 - The `wrap*` methods are moved to the `OffloadWrapper` class.
 - The `OffloadWrapper` includes `Suffix` and `EmitSurfacesAndTextures` fields
to specify some additional options.
 - The `Suffix` field is used when emitting the descriptor, registration methods,
etc, to make them more readable. It is empty by default.
 - The `EmitSurfacesAndTextures` field controls whether to emit surface and
texture registration code, as those functions were removed from `CUDART`
in CUDA 12. It is true by default.
 - The `wrap*` methods now have an optional field to specify the `EntryArray`;
this change is needed to enable JIT compilation, as ORC doesn't fully support
`__start_` and `__stop_` symbols. Thus, to JIT the code, the `EntryArray` has
to be constructed explicitly in the IR.
 - The function `getOffloadingEntryInitializer` was added to help create the
`EntryArray`, as it returns the constant initializer and not a global variable.