Promote and round operations

[mazimkhan]

Adding additional rounding variants of promotion and demotion operations for arm_sve-inl.h and generic_ops-inl.h:

• DemoteCeilTo rounds each element up before converting the rounded value to half-width a signed or unsigned integer.
• DemoteFloorTo rounds each element down before converting the rounded value to half-width a signed or unsigned integer.
• PromoteCeilTo rounds each element up before converting the rounded value to a signed or unsigned integer.
• PromoteFloorTo rounds each element down before converting the rounded value to a signed or unsigned integer.
• PromoteToNearestInt rounds each element towards the nearest integer, with ties to even, and converts the rounded value to a signed or unsigned integer.
• MaskedDemoteToOrZero demotes each element where the mask is set and returns zero for each inactive lane.
• MaskedPromoteToOrZero promotes each element where the mask is set and returns zero for each inactive lane.

Tests have been added for the operations.