Drop-in mobx-state-tree API compatibility

[jrmyio]

I tried updating all mobx-state-tree references to mobx-quick-tree. However, I ran into serveral issues where some features /exports are missing:

1. types.numberIdentifier

2. .preProcessSnapshot and .postProcessSnapshot

3. import { typecheck, castToReferenceSnapshot } from '@gadgetinc/mobx-quick-tree';

4. import type { ReferenceIdentifier, } from '@gadgetinc/mobx-quick-tree';

There might be more type related incompatbilities but 1) and 2) seemed are not type related and probably most important.

[airhorns]

Thanks for reporting this! Want to send a PR?