Test hover against the hit rect, not the bare frame rect

CreateBackdrop widens a frame's hit rect by the border, so mouse focus
and OnEnter/OnLeave cover a band that plain MouseIsOver reports as
outside. Add MouseIsOverHitRect, which passes the frame's hit rect
insets as MouseIsOver offsets, and use it at the unpadded call sites.
The XP bar's hover text follows the same OnEnter/OnLeave flag as its
fade.

api/ui-widgets.lua

@@ -661,7 +661,7 @@ function pfUI.api.SkinButton(button, cr, cg, cb, icon, disableHighlight)
   end
 
   b.UnlockHighlight = function()
-    if not MouseIsOver(b) then
+    if not MouseIsOverHitRect(b) then
       b:SetBackdropBorderColor(GetStringColor(pfUI_config.appearance.border.color))
     end
     b.locked = false
@@ -1175,7 +1175,7 @@ function pfUI.api.CreateInfoBox(text, time, parent, height)
 
       if GetTime() > infobox.lastshow + infobox.duration then
         if not infobox.fade:IsPlaying() then infobox.fade:Play() end
-      elseif MouseIsOver(this) then
+      elseif MouseIsOverHitRect(this) then
         this:SetAlpha(max(0.4, this:GetAlpha() - .1))
       else
         this:SetAlpha(min(1, this:GetAlpha() + .1))