Add possibility to invert Area series filled area

[kirchet]

Is your feature request related to a problem? Please describe.

Add possibility to fill top area instead of bottom

Describe the solution you'd like

Add an addtional option like invertFilledArea to AreaStyleOptions.

lightweight-charts/src/model/series-options.ts

Lines 210 to 287 in f28f811

	/**
	* Represents style options for an area series.
	*/
	export interface AreaStyleOptions {
	/**
	* Color of the top part of the area.
	*
	* @defaultValue `'rgba( 46, 220, 135, 0.4)'`
	*/
	topColor: string;
	/**
	* Color of the bottom part of the area.
	*
	* @defaultValue `'rgba( 40, 221, 100, 0)'`
	*/
	bottomColor: string;
	/**
	* Line color.
	*
	* @defaultValue `'#33D778'`
	*/
	lineColor: string;
	/**
	* Line style.
	*
	* @defaultValue {@link LineStyle.Solid}
	*/
	lineStyle: LineStyle;
	/**
	* Line width in pixels.
	*
	* @defaultValue `3`
	*/
	lineWidth: LineWidth;
	/**
	* Line type.
	*
	* @defaultValue {@link LineType.Simple}
	*/
	lineType: LineType;
	/**
	* Show the crosshair marker.
	*
	* @defaultValue `true`
	*/
	crosshairMarkerVisible: boolean;
	/**
	* Crosshair marker radius in pixels.
	*
	* @defaultValue `4`
	*/
	crosshairMarkerRadius: number;
	/**
	* Crosshair marker border color. An empty string falls back to the the color of the series under the crosshair.
	*
	* @defaultValue `''`
	*/
	crosshairMarkerBorderColor: string;
	/**
	* The crosshair marker background color. An empty string falls back to the the color of the series under the crosshair.
	*
	* @defaultValue `''`
	*/
	crosshairMarkerBackgroundColor: string;
	/**
	* Last price animation mode.
	*
	* @defaultValue {@link LastPriceAnimationMode.Disabled}
	*/
	lastPriceAnimation: LastPriceAnimationMode;
	}