Add reference types R32 and R64

-Add resumable_trap, safepoint, isnull, and null instructions
-Add Stackmap struct and StackmapSink trait

Co-authored-by: Mir Ahmed <mirahmed753@gmail.com>
Co-authored-by: Dan Gohman <sunfish@mozilla.com>

cranelift/filetests/src/test_binemit.rs

@@ -11,6 +11,7 @@ use cranelift_codegen::dominator_tree::DominatorTree;
 use cranelift_codegen::flowgraph::ControlFlowGraph;
 use cranelift_codegen::ir;
 use cranelift_codegen::ir::entities::AnyEntity;
+use cranelift_codegen::isa;
 use cranelift_codegen::print_errors::pretty_error;
 use cranelift_codegen::settings::OptLevel;
 use cranelift_reader::TestCommand;
@@ -100,9 +101,15 @@ impl binemit::CodeSink for TextSink {
     fn begin_jumptables(&mut self) {
         self.code_size = self.offset
     }
-
     fn begin_rodata(&mut self) {}
     fn end_codegen(&mut self) {}
+    fn add_stackmap(
+        &mut self,
+        _: &[ir::entities::Value],
+        _: &ir::Function,
+        _: &dyn isa::TargetIsa,
+    ) {
+    }
 }
 
 impl SubTest for TestBinEmit {