fix(stubs): Pass stubbed function to function props

The original implementation, added in
22c7698, passed a string value to a
function prop. This instead passes an actual function, which stringifies
to the same string.

The problem with the previous approach is that Vue started warning about
strings passed to function props in
vuejs/core@7ccd453.
As a result, this produced excessive noise in the logs that the author
can do nothing about.

Author: markrian

src/vnodeTransformers/stubComponentsTransformer.ts

@@ -42,6 +42,9 @@ interface StubOptions {
   renderStubDefaultSlot?: boolean
 }
 
+function stubbedFunctionProp() {}
+stubbedFunctionProp.toString = () => '[Function]'
+
 const normalizeStubProps = (props: ComponentPropsOptions) => {
   // props are always normalized to object syntax
   const $props = props as unknown as ComponentObjectPropsOptions
@@ -51,7 +54,7 @@ const normalizeStubProps = (props: ComponentPropsOptions) => {
       return { ...acc, [key]: [value?.toString()] }
     }
     if (typeof value === 'function') {
-      return { ...acc, [key]: ['[Function]'] }
+      return { ...acc, [key]: [stubbedFunctionProp] }
     }
     return { ...acc, [key]: value }
   }, {})