feat: add overridable storage service

[nihonium-cfx]

A followup for #153 (comment)

With this new override one can provide monaco with data for it's storage service, which is, among others, responsible for storing cached theme data. This allows for monaco to restore theme colors without flickering through default theme first, if you supply the storage data it asked you store before, of course.

Example usage:

// The settings.json file needs to be written ASAP
registerServiceInitializeParticipant(async (accessor) => {
  // import { writeFile } from 'vscode/monaco'
  await writeFile(URI.from({ schema: 'user', path: '/settings.json' }), `
  {
    "workbench.colorTheme": "Monokai",
  }
  `);
});

await initialize({
  ...getStorageServiceOverride({
    read(scope) {
      try {
        const data = JSON.parse(localStorage[`__STORAGE__${scope}__`]);

        return new Map(data);
      } catch (e) {
        return new Map();
      }
    },
    async write(scope, data) {
      localStorage[`__STORAGE__${scope}__`] = JSON.stringify(Array.from(data));
    }
  }),
});

[nihonium-cfx]

I think it's better to address init sequence concerns in another PR