getLinesTotalHeight() {
        this._checkPendingChanges();
        const linesHeight = this._lineHeight * this._lineCount;
        const whitespacesHeight = this.getWhitespacesTotalHeight();
        return linesHeight + whitespacesHeight + this._paddingTop + this._paddingBottom;
    }
Get the sum of heights for all objects.

@return The sum of heights for all objects.