[bindings/go] Add Go bindings to LLVMGetIndices

Summary: This instruction is useful for inspecting extractvalue/insertvalue in IR. Unlike most other operations, indices cannot be inspected using the generic Value.Opcode() function so a specialized function needs to be added.

Reviewers: whitequark, pcc

Reviewed By: whitequark

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53883

llvm-svn: 346388