Properly merge incoming props (#1265)

* rename inconsistent `passThroughProps` and `passthroughProps` to more
concise `incomingProps`

This is going to make a bit more sense in the next commits of this
branch, hold on!

* split props into `propsWeControl` and `propsTheyControl`

This will allow us to merge the props with a bit more control. Instead
of overriding every prop from the user' props with our props, we can now
merge event listeners.

* update `render` API to accept `propsWeControl` and `propsTheyControl`

* improve the merge logic

This will essentially do the exact same thing we were doing before:
```js
let props = { ...propsTheyControl, ...propsWeControl }
```

But instead of overriding everything, we will merge the event listener
related props like `onClick`, `onKeyDown`, ...

* fix typo in tests

* simplify naming

- Rename `propsWeControl` to `ourProps`
- Rename `propsTheyControl` to `theirProps`

* update changelog

packages/@headlessui-react/src/components/label/label.tsx

@@ -88,22 +88,28 @@ export let Label = forwardRefWithAs(function Label<
   },
   ref: Ref<HTMLLabelElement>
 ) {
-  let { passive = false, ...passThroughProps } = props
+  let { passive = false, ...theirProps } = props
   let context = useLabelContext()
   let id = `headlessui-label-${useId()}`
   let labelRef = useSyncRefs(ref)
 
   useIsoMorphicEffect(() => context.register(id), [id, context.register])
 
-  let propsWeControl = { ref: labelRef, ...context.props, id }
+  let ourProps = { ref: labelRef, ...context.props, id }
 
-  let allProps = { ...passThroughProps, ...propsWeControl }
-  // @ts-expect-error props are dynamic via context, some components will
-  //                  provide an onClick then we can delete it.
-  if (passive) delete allProps['onClick']
+  if (passive) {
+    if ('onClick' in ourProps) {
+      delete (ourProps as any)['onClick']
+    }
+
+    if ('onClick' in theirProps) {
+      delete (theirProps as any)['onClick']
+    }
+  }
 
   return render({
-    props: allProps,
+    ourProps,
+    theirProps,
     slot: context.slot || {},
     defaultTag: DEFAULT_LABEL_TAG,
     name: context.name || 'Label',