X86ISelDAGToDAG: Transform TEST + MOV64ri to SHR + TEST

Optimize a pattern where a sequence of 8/16 or 32 bits is tested for
zero: LLVM normalizes this towards and `AND` with mask which is usually
good, but does not work well on X86 when the mask does not fit into a
64bit register. This DagToDAG peephole transforms sequences like:

```
movabsq $562941363486720, %rax # imm = 0x1FFFE00000000
testq %rax, %rdi
```

to

```
shrq $33, %rdi
testw %di, %di
```

The result has a shorter encoding and saves a register if the tested
value isn't used otherwise.

Differential Revision: https://reviews.llvm.org/D121320