Documentation for some fields

For code review https://github.com/phetsims/greenhouse-effect/issues/331 ...

Code documentation is generally excellent. There are a few places where explanation of fields would be useful.

[x] EnergyInfoQueueItem.ts

public readonly dt: number;
public readonly energy: number;

[x] PhotonCrossingTestResult.ts

public static readonly FULLY_ABOVE = new PhotonCrossingTestResult();
public static readonly FULLY_BELOW = new PhotonCrossingTestResult();
public static readonly CROSSED_BUT_IGNORED = new PhotonCrossingTestResult();
public static readonly CROSSED_AND_ABSORBED = new PhotonCrossingTestResult();
public static readonly NONE = new PhotonCrossingTestResult();

[x] PhotonCollection.ts - maybe not all of these, but the ones that are not obvious.

public readonly photons: ObservableArray<Photon>;
public readonly photonAbsorbingEmittingLayers: PhotonAbsorbingEmittingLayer[];
public readonly showAllSimulatedPhotonsInViewProperty: BooleanProperty;
private readonly sunEnergySource: SunEnergySource;
private readonly groundLayer: GroundLayer;
private readonly glacierPresentProperty: TReadOnlyProperty<boolean>;
private photonCreationCountdown: number;
private groundPhotonProductionRate: number;
private groundPhotonProductionTimeAccumulator: number;
private visiblePhotonCreationCount: number;
private infraredPhotonCreationCount: number;

[x] EnergyBalanceSoundGenerator.ts

private interBlipTime: number = Number.POSITIVE_INFINITY;
private interBlipCountdown: number = Number.POSITIVE_INFINITY;

[x] PhotonSprites.ts

private readonly photonScale: number;
private readonly visiblePhotonSprite: Sprite;
private readonly infraredPhotonSprite: Sprite;

[x] WavesModel.ts - maybe not all of these, but the ones that are not obvious.

public readonly waveGroup: PhetioGroup<Wave, WaveCreatorArguments>;
public readonly wavesChangedEmitter: TEmitter;
private readonly sunWaveSource: SunWaveSource;
private readonly groundWaveSource: GroundWaveSource;
private cloudReflectedWavesMap: Map<Wave, Wave>;
private glacierReflectedWavesMap: Map<Wave, Wave>;
private readonly atmosphereLayerToXRangeMap: Map<EnergyAbsorbingEmittingLayer, Range>;
public readonly waveAtmosphereInteractions: ObservableArray<WaveAtmosphereInteraction>;
private readonly waveLineStart: Vector2;
private readonly waveLineEnd: Vector2;
private readonly waveLine: Line;
private readonly atmosphereLineStart: Vector2;
private readonly atmosphereLineEnd: Vector2;
private readonly atmosphereLine: Line;

[x] WaveSourceSpec.ts

public readonly xPosition: number;
public readonly propagationDirection: Vector2;

[x] WavesCanvasNode.ts

type RenderingParameters = {
  baseColorProperty: ColorProperty;
  amplitude: number;
  wavelength: number;
};
…
private readonly waveRenderingParameters: Map<number, RenderingParameters>;

phetsims / greenhouse-effect

Documentation for some fields #338