[XLA:MSA] Refactor `MsaAlgorithm` out of `memory_space_assignment.h/cc` files.
[XLA:MSA] Refactor `MsaAlgorithm` out of `memory_space_assignment.h/cc` files.
1. Move `MsaAlgorithm` to `algorithm.h/cc` files under `memory_space_assignment` directory.
1. Move `AllocationValue`, `AsynchronousCopyOrdering`, `AsynchronousCopyResource`, `AsynchronousCopy` to `algorithm.h/cc`.
1. Change remaining usages of `BufferInterval` and `BufferIntervalCompare` to `MsaBufferInterval` and `MsaBufferIntervalCompare`
1. Move functions related to AllocationSequence in allocation.h/cc
