[InstCombine] For vector extract when extract vector and insert value type is the same

This patch has implements these optimizations:

 extract.vector(insert.vector(Vector, Value, Idx), Idx) --> Value

 extract.vector(insert.vector(Vector, Value, InsertIndex), ExtractIndex)
  --> extract.vector(Vector, ExtractIndex)

Reviewed By: sdesmalen

Differential Revision: https://reviews.llvm.org/D132137