Allow to specify default dispatcher for formula.

[Laimiux]

What

By default, we process formula updates on a thread that emits the event. This pull request adds functionality to specify a default dispatcher which enables us to globally move all processing to a background thread.

You can specify a default dispatcher at the plugin level which will be applied to all formulas:

val myPlugin = object : Plugin {
    override fun defaultDispatcher(): Dispatcher = Dispatcher.Background 
}
FormulaPlugins.setPlugin(myPlugin)

Alternatively, you can specify default dispatcher for a single formula via toObservable or toFlow:

val runtimeConfig = RuntimeConfig(defaultDispatcher = Dispatcher.Background) 
val observable = formula.toObservable(input, runtimeConfig)

Not part of this pull request

In a follow-up pull request, we will add ability to control dispatcher for individual transitions.

Within an individual formula, a developer can specify Transition.ExecutionType such as Transition.Immediate to override the default behavior.

ButtonOutput(
    onSelected = context.callback(Transition.Immediate) { 
        transition { navigateToScreen() }
    }
)

Alternatively, it can also specify Transition.Background execution type for certain events

RxAction.fromObservable {}.onEvent(Transition.Background) { event ->
    val items = event.items.map { computeSomething() }
    transition(items)
}

[carrotkite]

	3 Warnings
⚠️	No coverage data found for com/instacart/formula/Action
⚠️	No coverage data found for com/instacart/formula/plugin/Plugin
⚠️	No coverage data found for com/instacart/formula/plugin/Dispatcher

JaCoCo Code Coverage 80.55% ✅

Class	Covered	Meta	Status
com/instacart/formula/coroutines/FlowRuntime	100%	0%	✅
com/instacart/formula/internal/FormulaManagerImpl	87%	0%	✅
com/instacart/formula/internal/ChildrenManager	75%	0%	✅
com/instacart/formula/internal/ListenerImpl	75%	0%	✅
com/instacart/formula/FormulaPlugins	80%	0%	✅
com/instacart/formula/FormulaRuntime	78%	0%	✅
com/instacart/formula/RuntimeConfig	80%	0%	✅
com/instacart/formula/Effect	100%	0%	✅
com/instacart/formula/Action	No coverage data found : -%	No coverage data found : -%	🃏
com/instacart/formula/test/RxJavaFormulaTestDelegate	90%	0%	✅
com/instacart/formula/plugin/Plugin	No coverage data found : -%	No coverage data found : -%	🃏
com/instacart/formula/plugin/Dispatcher	No coverage data found : -%	No coverage data found : -%	🃏

Generated by 🚫 Danger

[Laimiux]

Renamed from NoOp to None

[jasonostrander]

LGTM