Add Skeleton Loading View

[NikolaiMadlener]

Problem

SpeziViews lacks a skeleton loading component, leaving developers to handle loading states manually or with less polished solutions.

Solution

Add a reusable SwiftUI skeleton loading view to SpeziViews. It should support customizable layouts by leveraging a ViewBuilder closure to define custom placeholder shapes. Additionally, it should come with a shimmer effect/animation to enhance the loading experience.

Additional context

Proposal of what it could look like:

Code of Conduct

• I agree to follow this project's Code of Conduct and Contributing Guidelines

[PSchmiedmayer]

Nice, I like the idea. Could be combined with ViewState in a nice way that it provides some nice components for a .processing state.