codemirror: show indentation markers less vivid

[ildar170975]

Currently indentation markers (vertical lines) are shown of same color as a cursor.
A bit distracting, honestly.
Please show the marker with a less vivid color.

In this external js file a --divider-color is used:

import { css } from 'https://unpkg.com/@polymer/lit-element@latest/lit-element.js?module';

customElements.whenDefined('ha-code-editor').then(() => {
  const Editor = customElements.get('ha-code-editor');

  const newStyle = css`
  .cm-editor { --indent-marker-active-bg-color: var(--disabled-color); }`;

  const newStyles = [].concat(Editor.styles, newStyle);
  Object.defineProperty(Editor, 'styles',        {value: newStyles, configurable: true, enumerable: false});
  Object.defineProperty(Editor, 'elementStyles', {value: newStyles, configurable: true, enumerable: false});
});

Before:

With js file:

[ildar170975]

solved in #25045