Opt-out of Partial Load Mode for the App Designer

Currently the App Designer (project properties) is opted in to being deferred for Partial Load Mode, because the Resources editor, Settings editor, and one or more property pages, need to be deferred.

We want to change the code so that we can opt individual property pages or sub-editors in to waiting for PLM (note: Resources and Settings editor factories are both already opted in), and opt the main App Designer editor factory _out_ so that as much of the UI is accessible as it can be.

Steps:

* [x] Support deferred initialization in the app designer framework (PR: https://github.com/dotnet/project-system/pull/6299)
* [ ] Show the PLM waiting screen inside the property page host panel
* Blocked on: the SetParent call inside WindowFrame.cs is failing, [here](https://devdiv.visualstudio.com/DevDiv/_git/VS?path=%2Fsrc%2Fenv%2Fshell%2FWindowManager%2FWindowFrame.cs&version=GBmaster)
* Both HWNDs in the call above are valid, and have WM_CHILD set correctly, but debugging into this call was not successful when I tried
* [ ] Opt individual property pages in to PLM with ` on the com classes for the relevant property page
* [ ] Opt the app designer editor factory out of PLM in its `ProvideEditorFactory` attribute