compiler: reimplement interface type asserts

This is a big reimplementation that simplifies the compiler a lot.
Instead of storing the method set in metadata and lowering the type
asserts as a whole program pass, this change just puts the list of
methods in the type code (and a separate global for the interface type).

transform/rtcalls_test.go

@@ -22,11 +22,3 @@ func TestOptimizeStringEqual(t *testing.T) {
 		transform.OptimizeStringEqual(mod)
 	})
 }
-
-func TestOptimizeReflectImplements(t *testing.T) {
-	t.Parallel()
-	testTransform(t, "testdata/reflect-implements", func(mod llvm.Module) {
-		// Run optimization pass.
-		transform.OptimizeReflectImplements(mod)
-	})
-}