Add a reusable SwiftUI Toast

[pinarol]

Closes #344

From figma:

Description

• Adds an easily reusable toast view.
• Each toast is added to the toast queue by the business logic. The queue is observed by the ToastContainerView and reflected to UI.
• We can display multiple toast at a time.
• A Toast will dismiss itself after a while automatically.
• The toast duration is calculated according to a formula so longer messages will be displayed longer.
• Light & dark modes supported.

https://github.com/user-attachments/assets/3d89d702-7a1f-4d1f-a89f-27b761a2af9b

Testing Steps

• SwiftUI demo app > Avatar Picker > Change avatar

You can also play around with ToastContainerView preview.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Gravatar UIKit Prototype Build by scanning the QR code below to install the corresponding build.

	App Name	Gravatar UIKit Prototype Build
	Build Number	1077
	Version	1.0
	Bundle ID	com.automattic.gravatar-sdk-demo-uikit.prototype-build
	Commit	da8749cb26a4631fed378bc61eb0347dcf2b9a6f
	App Center Build	Gravatar SDK Demo - UIKit #26

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Gravatar SwiftUI Prototype Build by scanning the QR code below to install the corresponding build.

	App Name	Gravatar SwiftUI Prototype Build
	Build Number	1077
	Version	1.0
	Bundle ID	com.automattic.gravatar-sdk-demo-swiftui.prototype-build
	Commit	da8749cb26a4631fed378bc61eb0347dcf2b9a6f
	App Center Build	Gravatar SDK Demo - SwiftUI #25

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[pinarol]

.transition(.opacity.combined(with: .move(edge: .bottom)))

This looks nice. I am adding.

It would be great to have a dismiss by the swipe down gesture. I believe many people would try this by default as first attempt of dismissing (more than tapping in a button).

This is not a very simple thing to get right and not sure it should be in the 1st iteration. If we take care of the "must have" features timely we can tackle this I think. We can also consider "tap to any place to close" and keep things simple for now.

[pinarol]

Invalid frame dimension (negative or non-finite).

Seems like that line was unnecessary anyway so I removed it. The error is gone.

[pinarol]

Ready for another look @etoledom