Remove Legacy Gallery from SLNs

[PureWeen]

Description of Change

We're not longer using the Legacy Galleries so let's remove them from our SLNs. This should help load and build times a bit.

I moved the CG SLNF to a full SLN just in case we want to run the Legacy CGs at a later point in time. Ideally we will just delete all this code for net10 or later this year

[jsuarezruiz]

I think also need to update scripts removing the legacy gallery. For example:

maui/eng/devices/devices-shared.cake

Line 16 in f642447

["Compatibility.ControlGallery.Android"] = "Compatibility.ControlGallery.Android",

or

maui/eng/cake/dotnet.cake

Line 236 in f642447

Task("dotnet-legacy-controlgallery-ios")

And from the pipelines:

maui/eng/pipelines/ui-tests.yml

Line 165 in f642447

compatibilityAndroidApp: $(System.DefaultWorkingDirectory)/src/Compatibility/ControlGallery/src/Android/Compatibility.ControlGallery.Android.csproj

Lets merge this first, then we can still run the pipelines if we want/need. For now removing from SLN will reduce the load for people opening this on their machines.