[MVUX] Make all oprators fluent firendly

[dr1rrb]

What would you like to be added:

All operator (like State.ForEachAsync and State.Observe) should be fluent friendly so we don't have to declare them in ctor.

Why is this needed:

To improve code discoverability and readability.

For which Platform:

• [x] iOS
• [x] Android
• [x] WebAssembly
• [x] WebAssembly renders for Xamarin.Forms
• [x] Windows
• [ ] Build tasks

Anything else we need to know?

This means that we need to enable caching like for other operators such as Select