Declaration of war is not an attack

[jwrober]

Describe the bug
When you declare war on a player, for example while in Anarchy to Democracy, the game thinks you have attacked the player when you haven't.

To Reproduce
Steps to reproduce the behavior:

1. Get an alliance with two players to create a three-way alliance.
2. Player A goes to anarchy and declares war on Player B
3. Player C gets a message that Player A has attacked Player B, your Senate approves a resolution and you go from alliance to armistice w/ Player A.

Expected behavior
There should be a differentiation between an actual attack (units fighting each other) vs a war declaration.

Screenshots

Platform and version (please complete the following information):

• OS: Linux
• Freeciv21 version: 3.1-alpha.5
• Ruleset/Longturn game (if applicable): LTX

Additional context
Add any other context about the problem here.

[lmoureaux]

See also #2177.