housekeeping: Move UI functionality to Splat.Drawing

[glennawatson]

If users of Blazor/Uno and other .netcoreapp3.0 platforms attempt to compile on a non-windows platform at the moment there will be compile errors. This is due to UseWPF/UseWinForms being enabled on those platforms.

Separating the UI into a different class to allow those applications not to be affected.

Android is now minimum of 9.0

Fix bug in MS DI HasRegistrations

[codecov]

Codecov Report

Merging #403 into master will decrease coverage by 9.85%.
The diff coverage is 0.48%.

@@            Coverage Diff             @@
##           master     #403      +/-   ##
==========================================
- Coverage   71.51%   61.66%   -9.86%     
==========================================
  Files          66       70       +4     
  Lines        3697     4367     +670     
  Branches      338      420      +82     
==========================================
+ Hits         2644     2693      +49     
- Misses       1008     1596     +588     
- Partials       45       78      +33

Impacted Files	Coverage Δ
src/Splat.Drawing/Bitmaps/BitmapLoader.cs	0% <ø> (ø)
...lat.Drawing/Platforms/net4/Maths/RectExtensions.cs	0% <ø> (ø)
...lat.Drawing/Platforms/net4/Maths/SizeExtensions.cs	0% <ø> (ø)
...t.Drawing/Platforms/net4/Colors/ColorExtensions.cs	0% <ø> (ø)
...ing/Platforms/net4/Bitmaps/PlatformBitmapLoader.cs	0% <ø> (ø)
src/Splat.Drawing/Colors/KnownColors.cs	94.93% <ø> (ø)
...awing/Platforms/net4/Bitmaps/BitmapSourceBitmap.cs	0% <ø> (ø)
src/Splat.Drawing/Bitmaps/BitmapLoaderException.cs	0% <ø> (ø)
...rc/Splat/ServiceLocation/FuncDependencyResolver.cs	30.9% <ø> (ø)	⬆️
...wing/Platforms/net4/Colors/SplatColorExtensions.cs	0% <ø> (ø)
... and 43 more

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