This removes the insertvalue constant expression, as part of https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179. This is very similar to the extractvalue removal from D125795.
ConstantExpr::getInsertValue() can be replaced with IRBuilder::CreateInsertValue() or ConstantFoldInsertValueInstruction(), depending on whether a constant result is required (with the latter being fallible).
The ConstantExpr::hasIndices() and ConstantExpr::getIndices() methods also go away here, because there are no longer any constant expressions with indices.