Raid unitframes: add option to reverse group order (#75)

* Add raidreverse default to unitframes config

Defaults to off, so existing layouts are unchanged.

* Raid frames: add option to reverse group order

Read the new raidreverse setting and mirror the column index when placing raid frames, so group 1 sits on the far right and the following groups grow to the left.

* Add "Reverse Group Order" checkbox to raid settings

Placed under "Raid Fill Direction" in the raid frame options.
/pfui > Settings > Unit Frames > Raid > Layout

* Raid frames: rename reverse option to "Grow Right To Left"

The option mirrors columns in both fill directions, so name it for what
it does. Mirror across the columns maxraid can fill instead of the whole
layout, so smaller raids stay next to the anchor. Lay the raid grid out
through SlotToCoord like the pet grid, move the default next to the other
raid layout keys, and add the label to the locale tables.

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Co-authored-by: Brues <5278969+brues-code@users.noreply.github.com>

env/translations_enUS.lua

@@ -373,6 +373,7 @@ pfUI_translation["enUS"] = {
   ["Group Options"] = nil,
   ["Group-Pet"] = nil,
   ["Group-Target"] = nil,
+  ["Grow Right To Left"] = nil,
   ["Gryphon"] = nil,
   ["Gryphons"] = nil,
   ["Guild Online"] = nil,