[XLA:MSA] Remove unnecessary Extend() call in memory space assignment. This Extend() call would also lead to a memory assignment issue since it wasn't accompanied by the necessary chunk commit requests. We also add a VerifyAllocations() function that uses a BufferIntervalTree to check for overlapping Allocations before scheduling the asynchronous copies. This is an extra check for the correctness of MsaAlgorithm allocations, and is only applied if options_.verify is enabled in MSA options. options_.verify is disabled by default.

[XLA:MSA] Remove unnecessary Extend() call in memory space assignment. This Extend() call would also lead to a memory assignment issue since it wasn't accompanied by the necessary chunk commit requests. We also add a VerifyAllocations() function that uses a BufferIntervalTree to check for overlapping Allocations before scheduling the asynchronous copies. This is an extra check for the correctness of MsaAlgorithm allocations, and is only applied if options_.verify is enabled in MSA options. options_.verify is disabled by default. #15987