fix: prevent memory leak from theme recreation

[zukmkv]

There's a memory leak happening every time CodeMirror remounts; it duplicates styles because defaultThemeOption is recreated on every mount. It was fixed by adding a static reference to the extension with the .cm-scroller rule, and caching and reusing the other defaultThemeOption part that sets dimensions. Basically, when reused from the cache with the same widths and heights, we do not recreate the extension.
Below is the example without changes after several remounts:

However, there's still a thing that if you implement logic where you change dimensions (let's say only height) programmatically, they will not be replaced in the CSS but CodeMirror will just create an extra overriding class: