[mlir][sparse] Rename index_t to index_type again

[mlir][sparse] Rename index_t to index_type again

While testing LLVM 14.0.0 rc1 on Solaris, I ran into a compile failure:

                   from /var/llvm/llvm-14.0.0-rc1/rc1/llvm-project/mlir/lib/ExecutionEngine/SparseTensorUtils.cpp:22:
  /usr/include/sys/types.h:103:16: error: conflicting declaration ‘typedef short int index_t’
    103 | typedef short  index_t;
        |                ^~~~~~~
  In file included from
/var/llvm/llvm-14.0.0-rc1/rc1/llvm-project/mlir/lib/ExecutionEngine/SparseTensorUtils.cpp:17:
  /var/llvm/llvm-14.0.0-rc1/rc1/llvm-project/mlir/include/mlir/ExecutionEngine/SparseTensorUtils.h:26:7:
note: previous declaration as ‘using index_t = uint64_t’
     26 | using index_t = uint64_t;
        |       ^~~~~~~

The same issue had already occured in the past and fixed in D72619
<https://reviews.llvm.org/D72619>.  More detailed explanation can also be
found there.

Tested on `amd64-pc-solaris2.11` and `sparcv9-solaris2.11`.

Differential Revision: https://reviews.llvm.org/D119323