[InstCombine] Optimistically allow multiple shufflevector uses in foldOpPhi (#114278)

We would like to optimize situations of the form that happen after loop
vectorization+SROA:
```
loop:
%p

[InstCombine] Optimistically allow multiple shufflevector uses in foldOpPhi (#114278)

We would like to optimize situations of the form that happen after loop
vectorization+SROA:
```
loop:
%phi = phi zeroinitializer, %interleaved

%deinterleave_a = shufflevector %phi, poison ; pick half of the lanes
%deinterleave_b = shufflevector %phi, posion ; pick remaining lanes

... %a = ... %b = ...

%interleaved = shufflevector %a, %b ; interleave lanes of a+b
```
where the interleave and de-interleave shuffle operations cancel each
other out.
This could be handled by `foldOpPhi` but does not currently work because
it does
not proceed when there are multiple uses of the `Phi` operation.

This extends `foldOpPhi` to allow multiple `shufflevector` uses when
they are
shown to simplify for all `Phi` input values.

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