Fix duplicate territory listed for amphib bombardment

[asvitkine]

Change Summary & Additional Notes

This would happen when there's both an air and a land battle at the territory.
The cause was this coding pattern:

    for (final Territory t : battleTracker.getPendingBattleSites(false)) {
      final IBattle battle = battleTracker.getPendingBattle(t, BattleType.NORMAL);

Since getPendingBattleSites() would return battle sites for all (non-bombard) battles, it would list the same territory twice when that territory had both an air and a regular battle. But then, we'd retrieve the same NORMAL battle for that territory, processing it twice.

The fix is to get rid of the above pattern (which was also inefficient) and instead add a getPendingBattles(type) API.

Several other call sites are converted to the new pattern. It's possible they also exhibited related bugs.
The new pattern is also more efficient since it's no longer O(n^2) as the getPendingBattle() call is removed.

This PR also cleans up a few other things, such as grammar in comments that IntelliJ warns about.
Fixes #11999.

Release Note

FIX|Duplicate naval bombard territory listed when there's an air battle