[WebAssembly] Codegen for i64x2.extend_{low,high}_i32x4_{s,u}

Removes the builtins and intrinsics used to opt in to using these instructions
and replaces them with normal ISel patterns now that they are no longer
prototypes.

Differential Revision: https://reviews.llvm.org/D100402

GitOrigin-RevId: 6a18cc23efad410db48a3ccfc233d215de7d4cb9
3 files changed