Add new shorter predicates for testing machine operands for various types:

Add new shorter predicates for testing machine operands for various types:
e.g. MO.isMBB() instead of MO.isMachineBasicBlock().  I don't plan on
switching everything over, so new clients should just start using the
shorter names.

Remove old long accessors, switching everything over to use the short
accessor: getMachineBasicBlock() -> getMBB(),
getConstantPoolIndex() -> getIndex(), setMachineBasicBlock -> setMBB(), etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45464 91177308-0d34-0410-b5e6-96231b3b80d8