Implement AArch64 backend to emit optimized instruction sequence for following newly proposed VectorOperations and APIs.

1) Vector.compress, Vector.expand and VectorMask.compress APIs.
   - Cross lane vector compress and expansion operations which works under the influence of an explicit mask.
   - Mask flavor of the API clubs together all the set bits/ lanes of mask.
2) VectorOperations.BIT_COUNT:
     - counting the number of one-bits
3) VectorOperations.LEADING_ZEROS_COUNT:
     - counting the number of leading zero bits
4) VectorOperations.TRAILING_ZEROS_COUNT:
    - counting the number of trailing zero bits
5) VectorOperations.REVERSE:
    - reversing the order of bits
6) VectorOperations.REVERSE_BYTES:
   - reversing the order of bytes
7) compress and expand bits
   - Semantics are based on Hacker's Delight section 7-4 Compress, or Generalized Extract.