[SimplifyCFG] Handle `llvm.assume` in `passingValueIsAlwaysUndefined` (#89929)

See the following example:
```
define i32 @test(i32 %cond) {
entry:
  switch i32 %cond, label %default [
    i32 0, label %case0
    i32 1, label %case1
    i32 2, label %case2
  ]

case0:
  br label %exit

case1:
  br label %exit

case2:
  br label %exit

default:
  br label %exit

exit:
  %bool = phi i1 [ false, %default ], [ true, %case0 ], [ true, %case1 ], [ true, %case2 ]
  %res = phi i32 [ 0, %default ], [ 1, %case0 ], [ 2, %case1 ], [ 3, %case2 ]
  call void @llvm.assume(i1 %bool)
  ret i32 %res
}
```
The edge `%default -> %bool` is dead since it will trigger an immediate
UB.

Alive2: https://alive2.llvm.org/ce/z/gywJiE

My benchmark shows many rust applications and some c/c++ applications
(e.g., arrow/php/qemu) will benefit from this patch :)

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