Opt-out of Partial Load Mode for the App Designer

[davidwengier]

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
  • 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 `<ProvidePropertyPage(DeferUntilIntellisenseIsReady := True)> on the com classes for the relevant property page
• [ ] Opt the app designer editor factory out of PLM in its ProvideEditorFactory attribute

[davkean]

Triage: This is figuring out what pages don't actually need design-time build results and stop blocking opening the AppDesigner while PLM/operation progress is in progress, and block pages that actually need operation progress.

[davidwengier]

Random notes found while debugging #5858:

• We need to opt both the ApplicationDesignerEditorFactory and PropPageDesignerEditorFactory out of PLM
• We need to have our own flag in the individual designer tabs to flag whether they need to wait for intellisense
• In the AppDesignerPanel.CreateDesigner method (or similar) we would check that flag to go down one of two paths, before calling OpenSpecificEditor:
  • If the flag is false, then continue as normal
  • If the flag is true, it means wait for intellisense, which means the CreateDesigner method should create the PartialLoadWindowFrame somehow.
  • It maybe be able to let the shell do it (can we temporarily have DeferUntilIntellisenseIsReady() [here](http://index/?query=%60DeferUntilIntellisenseIsReady()&rightProject=VS(Repo)&file=src%5Cenv%5Cmsenv%5Ccore%5Cvsshlsvc.cpp&line=7749) return true?)
  • We show the PartialLoadWindowFrame and hook up to the OnFrameViewReplaced event on the frame, and then show the real content at that point

[davidwengier]

Re: opting individual pages into defering, letting the shell do it will definitely be the easiest, we just have to come up with a way for that to happen. We can simply create a second PropPageDesignerEditorFactory that opts-in, and have specific property pages use that instead of the current factory, which opts out. The issue is knowing which pages to do it for, as they are deliberately lazy-loaded so its not trivial to read information from them.

A new registry entry under [$RootKey$\PropertyPages\{..page guid..}] for DeferUntilIntellisenseReady=1 might be the easiest way to go.