[LV] Update handling of scalable pointer inductions after b73d2c8c.

The dependent code has been changed quite a lot since 151c1443 which
b73d2c8c effectively reverts. Now we run into a case where lowering
didn't expect/support the behavior pre 151c1443 any longer.

Update the code dealing with scalable pointer inductions to also check
for uniformity in combination with isScalarAfterVectorization. This
should ensure scalable pointer inductions are handled properly during
epilogue vectorization.

Fixes #57912.

(cherry picked from commit 2c692d89)