intersectWithViewport(range) {
        const startLineNumber = Math.max(this.startLineNumber, range.startLineNumber);
        const endLineNumber = Math.min(this.endLineNumber, range.endLineNumber);
        if (startLineNumber > endLineNumber) {
            // entirely outside minimap's viewport
            return null;
        }
        return [startLineNumber, endLineNumber];
    }
Intersect a line range with `this.startLineNumber` and `this.endLineNumber`.