📚[DOCS]: Add documentation about Selector Type Safety

[markwhitfeld]

Description

With NGXS v18, we have started to push towards better type safety for selectors.
The challenge is that we have users who use old mechanisms that are not type-safe and they would need guidance on converting their code to a more type-safe equivalent. Not only that, but there is an opportunity here to showcase all of the different helpers available.

We should definitely cover:

• Use a StateToken instead of the State Class to select from a state
  • and the alternative of using createSelector with some type casting to wrap an existing State Class as a type-safe selector
    createSelector([MyState], s => s as MyStateModel)
• Using createPropertySelectors to create smaller slices of your state
• Using createPickSelector to optimise a selector that has fewer dependencies
• Using createMappedSelector to combine selectors for view models, etc.

[dmrickey]

If I have 20 different properties in my state, am I supposed to write 20 different selectors instead of just passing an inline function to the select statement? (more specifically regarding nested properties - I don't see that there are any shortcuts for creating those)

[markwhitfeld]

@dmrickey if you have the time, I would be interested to understand your use cases.
Reach out to me on the NGXS Discord or Slack and we can have a chat.

[dmrickey]

@markwhitfeld
The discord link doesn't appear to be a permanent link as it seems to be expired (or possibly just a bad link). I've joined the Slack, but the chances of me seeing a response there after today are minimal at best :/. My discord user name is claudekennilol. I'm available there practically 24/7.
I'd love to be able to join discord and ask questions that will be more visible than here on github issues.