[AArc64][GlobalISel] Fix legalizer assert for G_INSERT_VECTOR_ELT

We should moreElements <3 x s1> to <4 x s1> before we try to widen the element,
otherwise we end up with a <3 x s21> nonsense type.

(cherry picked from commit a01e9ce8)

Test has been changed from original commit due to a fallback in a G_BITCAST.
Added abort=2 so we can see partial legalization and check no crash.