[VPlan] Simplify select !c, x, y -> select c, y, x (#147268)

This is split off from #133993

On its own this simplification isn't that useful, but it allows us to
make the equivalent VPBlendRecipe optimisation more generic by operating
on VPInstructions.

In order to actually test this without #133993, I've had to also extend
the m_Not pattern matcher to also catch VPWidenRecipes, since I couldn't
really think of a straightforward way to create a VPInstruction::Select
with a negated condition.

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