Update Cranelift to 0.52.0 (#710)

* Add unimplemented stubs for Cranelift interfaces

Cranelift changes to FuncEnvironment, TargetEnvironment, and GlobalInit (see https://github.com/bytecodealliance/cranelift/pull/1073) require these changes to compile wasmtime.

* Upgrade Cranelift to 0.52.0

crates/runtime/src/instance.rs

@@ -1253,6 +1253,7 @@ fn initialize_globals(instance: &mut Instance) {
                 unsafe { *to = *from };
             }
             GlobalInit::Import => panic!("locally-defined global initialized as import"),
+            GlobalInit::RefNullConst => unimplemented!(),
         }
     }
 }