Deprecate Swup for 2.x, remove it for 3.x

[Kocal]

Symfony UX Swup is the kind of package we do not want anymore on UX:

• ~20 lines of PHP (an empty Bundle and some configuration for the AssetMapper)
• and a small glue of JavaScript to the library

This kind of package does not bring any value, unlike UX Turbo, UX Map, etc... and can easily be re-created in the user's application:

1. install some dependencies through npm or importmap:require
2. either import swup library in their main entry (or create a stimulus controller)
3. and that's all

I suggest we deprecate it in 2.x, and remove it for 3.x.

• Deprecate: [Swup] Deprecate the package #2814
• Remove: [Swup] Remove package #2985

[weaverryan]

Agreed: swup is easy to set up & UX prefers Turbo

[smnandre]

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