Display RadarEvents on minimap

[charliefoxtwo]

The Radar class is now set up to track and display RadarEvents - we just need to do so.

Radar.RadarEvents has the list of events. It's a circular buffer. Events should be updated with whether they are currently playing when drawn.

https://github.com/OpenSAGE/OpenSAGE/blob/17db1bffbc42e0cf9f6bdee98e18ecedea50c6a1/src/OpenSage.Game/Radar.cs#L19

Radar events are a triangle with two colors forming a gradient along each edge. The triangle starts large (larger than the minimap), rotates clockwise, quickly shrinks down to its final size (whatever that is), and then fades out for the last 15 frames (captured within the RadarEvent object). I wasn't able to find any parameters in the inis which define the rotation rate or size of the triangle.

Events can be added with AddRadarEvent. https://github.com/OpenSAGE/OpenSAGE/blob/17db1bffbc42e0cf9f6bdee98e18ecedea50c6a1/src/OpenSage.Game/Radar.cs#L70

The user should be able to jump the camera to the last radar event by pressing the spacebar. The last radar event can be retrieved with TryGetLastEventLocation (this will return false if there are no prior events, such as at the start of the game). https://github.com/OpenSAGE/OpenSAGE/blob/17db1bffbc42e0cf9f6bdee98e18ecedea50c6a1/src/OpenSage.Game/Radar.cs#L84

Event animation can be marked as complete with StopAnimationForEvent. https://github.com/OpenSAGE/OpenSAGE/blob/17db1bffbc42e0cf9f6bdee98e18ecedea50c6a1/src/OpenSage.Game/Radar.cs#L97