Add host API for alltoallmem_on_stream collective operation (#333)

* Add host-side rocshmem_alltoallmem_on_stream function

Function signature:
  rocshmem_alltoallmem_on_stream(rocshmem_team_t team, void *dest,
                                 const void *source, size_t size,
                                 hipStream_t stream)

- The function launches rocshmem_alltoallmem_kernel which calls
device-side alltoall<char> workgroup collective through default context.
- Uses dynamic block size determination via occupancy API.
- Implemented for all backends.

* Fix incorrect sync buffer size allocation for alltoall in GDA and IPC backends

When allocating memory for alltoall_pSync_pool in setup_teams() and
teams_init() functions, the code incorrectly used ROCSHMEM_BCAST_SYNC_SIZE
instead of ROCSHMEM_ALLTOALL_SYNC_SIZE.

* Add functional test for team_alltoallmem_on_stream

This commit adds a new functional test to verify the correctness of
the host-side rocshmem_team_alltoallmem_on_stream API.

* Add documentation for rocshmem_alltoallmem_on_stream

This commit adds API documentation for the host-side
rocshmem_alltoallmem_on_stream function in the collective routines
section. The documentation includes:

[ROCm/rocshmem commit: 5577feb70d]

projects/rocshmem/tests/functional_tests/tester_arguments.cpp

@@ -182,7 +182,8 @@ void TesterArguments::get_arguments() {
       (type != TeamBroadcastTestType) && (type != PingAllTestType) &&
       (type != TeamBarrierTestType) && (type != TeamWAVEBarrierTestType) &&
       (type != TeamWGBarrierTestType) && (type != TeamCtxInfraTestBlockType) &&
-      (type != TeamCtxInfraTestOddEvenType)) {
+      (type != TeamCtxInfraTestOddEvenType) &&
+      (type != TeamAlltoallmemOnStreamTestType)) {
     if (numprocs != 2) {
       if (myid == 0) {
         std::cerr << "This test requires exactly two processes, we have "