[Moore] Input triggers assertion in canonicalizer infra

Nobody has claimed this yet.

`circt-opt -canonicalize` triggers an assertion on the following input. Maybe an upstream bug?

`Assertion failed: (mayBeGraphRegion(*op->getParentRegion()) && "expected that op has no uses"), function operator(), file PatternMatch.cpp, line 182.`

```
module {
moore.module private @snitch_regfile(in %clk_i : !moore.l1, in %raddr_i : !moore.array<2 x l5>, out rdata_o : !moore.array<2 x l32>, in %waddr_i : !moore.array<1 x l5>, in %wdata_i : !moore.array<1 x l32>, in %we_i : !moore.l1) {
%0 = moore.constant 1 : i32
%1 = moore.constant 0 : i32
%rdata_o = moore.variable : >
moore.procedure always_ff {
cf.br ^bb1(%1 : !moore.i32)
^bb1(%3: !moore.i32): // 2 preds: ^bb0, ^bb6
moore.return
^bb2: // no predecessors
cf.br ^bb4
^bb3: // no predecessors
cf.br ^bb4
^bb4: // 2 preds: ^bb2, ^bb3
%4 = moore.add %4, %0 : i32
cf.br ^bb6
^bb5: // no predecessors
cf.br ^bb6
^bb6: // 2 preds: ^bb4, ^bb5
%5 = moore.add %3, %0 : i32
cf.br ^bb1(%5 : !moore.i32)
}
%2 = moore.read %rdata_o : >
moore.output %2 : !moore.array<2 x l32>
}
}
```

Run circt-opt -canonicalize on the provided reproducer and inspect the assertion in PatternMatch.cpp at line 182, then trace the canonicalizer operation handling that reaches it. Done means the input no longer triggers the assertion and the failure is covered by a regression test.

Written by the indexing model from the issue text.