`TriggerProperty.valueFlow` emits an initial `TriggerUnit`, forcing every consumer to call `drop(1)`

Description

Every ViewModelProperty type in rive-android – Boolean, Number, Enum, String, and Trigger – is implemented so that its valueFlow sends one initial element as soon as the flow is collected:

This behaviour means that UI code like collect { … } or collectAsStateWithLifecycle() executes once immediately when the screen appears, even though the user has not triggered anything. Developers therefore have to remember to append .drop(1) (or a custom filter) every time they collect one of these flows.

Reproduction

Trigger example

val vmi = rive.controller.activeArtboard!!.viewModelInstance

coroutineScope.launch {
    vmi.getTriggerProperty("sampleTrigger")
        .valueFlow          // emits TriggerUnit once on collection
        .collect { println("sampleTrigger fired!") }
}

Output on first composition:

sampleTrigger fired!   // unexpected

Boolean example

coroutineScope.launch {
    vmi.getBooleanProperty("sampleFlag")
        .valueFlow          // emits current value once on collection
        .collect { value -> println("sampleFlag = $value") }
}

Expected behaviour

Provide a way to opt out of the initial emission:

Device & versions

Start at the ViewModelProperty implementations and the valueFlow entry point, especially getTriggerProperty("sampleTrigger"). Reproduce collection of the trigger flow and compare it with the Boolean example. Done means the chosen API provides a reliable way to avoid the initial TriggerUnit while preserving the intended behavior for existing value flows.