feat: allow for plugins being passed down as props to <open-scd>

[juancho0202]

Closes #1418

[pascalwilbrink]

The .plugins property is not adhering to the .plugins property structure of OpenSCD/core

[Stef3st]

This PR does met the acceptance criteria described in issue #1418 but most of the tasks described there have not been done. The Plugging mixin was supposed to be removed and a plugin interface should be exported in the Core's foundation file.

If these tasks are still valid then these changes need to be made. Otherwise the issue needs to be revised.

[Stef3st]

Looks good, got a few (small) remarks and a few questions. As stated in the meetings, this PR will have a follow up to no longer merge the 2 plugin interfaces (#1503)

@Stef3st is not part of the team and so I cannot request his time to do any reviews on open-scd

[juancho0202]

I added a reactive property _sortedStoredPlugins in order to overcome a lifecycle problem I was experiencing by passing down to the Layout addon the sortedStoredPlugins getter like this:

<oscd-layout
  .host=${this}
  .doc=${this.doc}
  .docName=${this.docName}
  .editCount=${this.editCount}
  .plugins=${this.sortedStoredPlugins} // <-- When plugins were added to the localStorage this getter wouldn't force a rerender
>
</oscd-layout>

I ended up moving the storePlugins function into the OpenSCD class and triggering a change to the reactive prop after the localStorage is updated like this:

private get sortedStoredPlugins(): Plugin[] {
  return this.storedPlugins
    .map(plugin => {
      if (!plugin.official) return plugin;
      const officialPlugin = (officialPlugins as Plugin[])
        .concat(this.parsedPlugins)
        .find(needle => needle.src === plugin.src);
      return <Plugin>{
        ...officialPlugin,
        ...plugin,
      };
    })
    .sort(compareNeedsDoc)
    .sort(menuCompare);
}

@state()
_sortedStoredPlugins: Plugin[] = [];

private storePlugins(plugins: Array<Plugin | InstalledOfficialPlugin>) {
  localStorage.setItem('plugins', JSON.stringify(plugins.map(withoutContent)));
  this._sortedStoredPlugins = this.sortedStoredPlugins;
}

And then the reactive property _sortedStoredPlugins is passed down to the Layout like this:

<oscd-layout
  .host=${this}
  .doc=${this.doc}
  .docName=${this.docName}
  .editCount=${this.editCount}
  .plugins=${this._sortedStoredPlugins}
>
</oscd-layout>

@pascalwilbrink let me know if you agree with my approach here, these were some tricky merge conflicts. Thanks for the review.