Update to SuiteSparse 6.0

[dweindl]

Relevant changes:

* major update: using CMake build system for all packages
* CMake Find*: all packages now have a Find*.cmake.  See
    SuiteSparse_config/cmake_modules.
* integers: int (32-bit) and SuiteSparse_long (nominally 64-bit) replaced
    with int32_t and int64_t.  The SuiteSparse_long #define has been
    deprecated and removed.  Replace its use with int64_t in any code that
    uses SuiteSparse v6.0.0 or later.  This is unlikely to change any
    use of any SuiteSparse package, but since it's possible that
    SuiteSparse_long was 32-bits on some platforms, the SO_VERSIION of
    all packages has been increased by one.

Will enable simplified CMake-based builds, and we probably won't need our modifications in SuiteSparse to match SUNDIALS types (#1733).