Move all the currently externally linked XML docs (for example /// <include file="../../docs/Microsoft.Maui.Controls/Accelerator.xml" path="Type[@FullName='Microsoft.Maui.Controls.Accelerator']/Docs/*" />) to inline in the source code.

• Make sure to adhere to https://github.com/dotnet/maui/blob/main/docs/CodeDocumentationGuidelines.md
• If there is extensive code samples, remove those
• Make sure the documentation is still relevant
• Make sure the documentation is useful
• If documentation is added to a bindable property, suffix with: "This is a bindable property." at the end of the <summary> tag.