Freeciv-3.3 updates to tileset format

[cazfi]

This is meant to be a bit similar thread to what we have about ruleset changes on the ruleset forum. Tileset format just usually changes much much less than ruleset format.

[cazfi]

Focus unit selection animation can now have any number of frames. Previously it was hardcoded to 4. RM #1012

[cazfi]

Action decision want icon can be animated RM #1013

While animating the action decision want icon isn't big feature in itself, this is an important step towards animation framework in general.

Animations other than the focus unit selection are not supported in clients other than gtk4.

[cazfi]

Extras of extra styles "Single1" and "Single2" can be animated RM #1096