[LV] Update logic for calculating register usage due to invariants

[LV] Update logic for calculating register usage due to invariants

Previously, while calculating register usage due to invariants, it was assumed that invariant would always be part of widening
instructions. This resulted in calculating vector register types for vectors which cant be legalized(check the newly added test for more details).

An invariant might not always need a vector register. For e.g., invariant might just be used for iteration check.

This patch checks if the invariant is part of any widening instruction and considers register usage accordingly. Fixes issue 60493

Differential Revision: https://reviews.llvm.org/D143422