[SYCL-MLIR] Handle accesses of structure of vector

[whitneywhtsang]

Since #7706, we decided to not add types under sycl::detail namespace in SYCL dialect.
So sycl::detail::Boolean is represented as llvm structure of vector type.

Pointer of struct is represented as llvm.ptr<struct<...>>, instead of memref<?xstruct<...>>.
Accessing element of the struct uses llvm.getelementptr, which produces llvm.ptr.
If an element of the struct is vector, then pointer to it would be llvm.ptr<vector>.

Pointer of SYCL type is represented as memref<?x!sycl...>.
Accessing element of the SYCL type uses polygeist.subindex, which produces memref.
If an element of the SYCL type is vector, e.g., !sycl.vec, then pointer to it would be memref<vector>.

We need to modify some code that does vector handling, as llvm.ptr<vector> is possible.

[whitneywhtsang]

Depends on #7706. Will rebase after #7706 get merged.

[victor-eds]

I propose replacing this test with a non-SYCL one in the parent directory. Instead of using sycl::detail::Boolean, I'd define a VecWrapper structured type holding an ext vector and store an ext vector of such type in it.

[whitneywhtsang]

I propose replacing this test with a non-SYCL one in the parent directory. Instead of using sycl::detail::Boolean, I'd define a VecWrapper structured type holding an ext vector and store an ext vector of such type in it.

I created a generic test case, but it is still in sycl, as we need to test when default addrspace is different.

[victor-eds]

LGTM

[victor-eds]

I'd also change the commit message to make it more generic (not a particular Detail::Boolean issue after all)