Add docs about animation methods and native mode

[daun]

• Add documentation for native option
• Create page "Defining animations" that explains different animation methods
• Add examples for each: CSS + JS + Native + None
• Add View Transition Support to v4 releases notes: great place to advertise this
• Update wording to reflect that swup supports many animation methods
• Should only be merged once swup 4.5 is released

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