Xamarin.forms: Replace all occurrences of FileImageSource with ImageSource

[rogihee]

Description

In order to be able to use other image sources such as SVG based ones all Core controls and renderers should use ImageSource instead of FileImageSource.

When the Core is updated, renderers should also be updated to never assume a FileImageSource.

These are the occurrences I could track down in Core and other Platform renderers:

Core

1. Button.Image
2. MenuItem.Icon
3. NavigationPage.TitleIcon
4. Page.Icon
5. Slider.ThumbImage

Android

1. NavigationPageRenderer toolbar icon
2. TabbedPageRendererer tab icon
3. ImageViewExtensions that is used by BaseCellView
4. Fastrenderers Button.Image
5. Platform title Icon

iOS

1. ButtonRenderer image
2. NagivationRenderer title image
3. SliderRenderer thumb image

UWP

None.

See also: #1955

[ysmoradi]

Any news?
+1

[groege]

Is there a way to speed this up? It shouldn't be that big of a change right?
Especially MenuItom.Icon would be VERY important for my project!

[MelbourneDeveloper]

Is this on its way?

[samhouts]

We haven't assigned the work yet, but we did investigate it as part of #4747. Unfortunately, it wasn't as trivial as hoped, so it is still a TODO item. We welcome a PR, if you're interested. Thanks!