setFontsize = size => {
      this.editorDiv.style.fontSize = `calc(${size}px * var(--total-scale-factor))`;
      this.translate(0, -(size - this.#fontSize) * this.parentScale);
      this.#fontSize = size;
      this.#setEditorDimensions();
    }
Update the font size and make this action as undoable.
@param {number} fontSize