Read FactionEncounterNumber from population tables

[John Snail]

Currently, the FactionEncounters builder reads FactionEncounterNumber from Text.txt, despite everything else to do with faction encounters having already been moved to population tables. Also see #12568.

For the most moddability, could the table look something like this? *Default would spawn either one kind of a creature multiple times, or multiple kinds of creatures, depending on how the table is laid out.

<population Name="FactionEncounterMembers_*Default">
  <object Blueprint="*Leader" />
  <object Blueprint="*Member" Number="3-6" />
</population>

<!-- Example -->
<population Name="FactionEncounterMembers_*Default">
  <object Blueprint="*Leader" />
  <group Name="Creatures" Style="pickone" Number="3-6">
    <object Blueprint="*Member" />
  </group>
</population>

‌