[FIX] props validation: do not subscribe to props keys

In dev mode, owl inserts an additional props validation step. Before
this commit, the validation would iterate on all key/value pairs of each
props. If the props is reactive, this has the unfortunate side effect of
subscribing the component to each of the keys, even though it should not
be.

This commit avoids the issue by only validating the raw object.

src/runtime/validation.ts

@@ -1,4 +1,5 @@
 import { OwlError } from "./error_handling";
+import { toRaw } from "./reactivity";
 
 type BaseType =
   | typeof String
@@ -84,6 +85,7 @@ export function validateSchema(obj: { [key: string]: any }, schema: Schema): str
   if (Array.isArray(schema)) {
     schema = toSchema(schema);
   }
+  obj = toRaw(obj);
   let errors = [];
   // check if each value in obj has correct shape
   for (let key in obj) {