Prevent shimmer animation from affecting initial layout of the view

[ast3150]

This introduces two changes:

1. Prevents the shimmer animation from propagating to the modified view
2. Delays the initial animation until the layout of the view is established so that the initial appearance of the view is not animated.

Fixes #19

[ikok07]

It's working great with this fix! Thank you :)

[vladyslavsosiuk]

hi @ast3150 could you check if the prior pr fixes the issue you are addressing for you?

[Mr-Fier-1]

@vladyslavsosiuk This prior pr fix, doesnt fix this Animation bug #19.

[vladyslavsosiuk]

Do you have steps to reproduce?

[Mr-Fier-1]

Sure!

import Shimmer
import SwiftUI

struct ContentView: View {
    var body: some View {
        NavigationView {  // Use NavigationStack here 
            VStack {
                Text("NavigationView")
                secondView()
            }
        }
    }
}

struct secondView: View {
    var body: some View {
        RoundedRectangle(cornerRadius: 15)
            .foregroundStyle(.red)
            .frame(width: 50, height: 50)

            .shimmering()
        Text("This is the second View")
            .redacted(reason: .placeholder)
            .shimmering()
    }
}

In my case the NavigationView and NavigationStack conflicted with the modifier.
When NavigationView was used this happened:

NavigationView.mp4

and with NavigationStack this:

NavigationStack.mp4

When using the changes from this MR, the visuals are as expected.

[daniel-tandem]

This PR fixes the issue I was seeing where I was trying to apply a shimmer on a view within a NavigationStack

[markiv]

Prevent shimmer animation from affecting initial layout of the view