Inconsistent number of tabs in sample apps

[mrlacey]

The sample app appears to be including output from all platforms.

Repro:

• Open CanvasLayout.sln in Visual Studio
• Run (Debug) CanvasLayout.WinAppSdk - See that there are 4 tabs included.
• Run (Debug) CanvasLayout.WinAppSdk again - See that there are now 5 tabs included.
• Run (Debug) CanvasLayout.UWP - See that there are 4 tabs included.
• Run (Debug) CanvasLayout.UWP again - See that there are still 4 tabs included.
• Run (Debug) CanvasLayout.WinAppSdk again - See that there are now 6 tabs included.
• Run (Debug) CanvasLayout.Wasm - See that there are 6 tabs included.
• Run (Debug) CanvasLayout.WinAppSdk again - See that there are now 7 tabs included.

I assume that wildcard paths are picking up files from the obj or bin directories from the other platform heads.

Possibly connected to #116

This also happens with the SizerBase experiment in #102 but the number of tabs there are even greater.
I haven't tested with the "All" solution.