* (insert|move|remove)ChildRenderObject Deprecation: Step 1
This deprecates the following methods:
* RenderObjectElement.insertChildRenderObject
* RenderObjectElement.moveChildRenderObject
* RenderObjectElement.removeChildRenderObject
...and replaces them with the following methods:
* RenderObjectElement.insertRenderObjectChild
* RenderObjectElement.moveRenderObjectChild
* RenderObjectElement.removeRenderObjectChild
The reason for the deprecation is to provide the `oldSlot` argument to
the `moveRenderObjectChild` method (such an argument was missing from
the now-deprecated `moveChildRenderObject` method) and the `slot`
argument to the `removeRenderObjectChild` method (such an argument was
missing from the now-deprecated `removeChildRenderObject` method). While
no argument was added to `insertRenderObjectChild`, the name change (and
corresponding deprecation) was made to maintain naming parity with the
other two methods.
This initial step does not update or remove any of the `slotToChild`
patterns that exist in the framework. This work is being separated
into two commits in case something needs to be reverted to minimize
the scope of each commit.
See https://github.com/flutter/flutter/issues/63269 for more info
