[SharpDX]comment fixes.

at Matrix.cs
[SharpDX] Add comments

to ViewportF class
[SharpDX]Added comments.

to Viewport.cs(also added Validate methods).
[SharpDX] Comment fixes.

+ small fixes to Viewport
[SharpDX]comment fixes.

at ViewportF.cs
[SharpDX]comment fixes.

at Viewport.cs - final
[SharpDX] Fix comments