Make Texture2D.Reload(Stream) public -- again

Someone already did this in a previous commit ( https://github.com/mono/MonoGame/commit/06f6c2fe65201fd3552af1261711af07fbc51cf3 ) but I think it inadvertently got lost in a merge...
I'm not sure why nobody missed it, but my team and I are using this method on Android, to recover from the GraphicsDevice.DeviceReset event. To quote the original commit message:

"The ContentManager class handles texture reloading of all it's loaded textures, but if you're using Texture2D.FromStream() to load textures, this change will allow you to reload them without updating their references everywhere."