fix(minimap-icon): ship BLP, point icon at .blp not .tga

WoW's texture engine only loads .blp — `SetTexture` (and LibDBIcon)
strips any extension and looks for foo.blp. The addon previously passed
`minimapicon.tga` and only shipped a .tga, so the engine fell back to
the green placeholder icon on the minimap button.

Convert assets/minimapicon.tga to a DXT3/BLP2 (alpha-encoding 1, the
format proven to decode on the CoA 3.3.5 client — DXT5 doesn't), ship
it alongside the .tga, and update the LibDBIcon NewDataObject 'icon'
field to reference the .blp.

Also normalises the path casing (Interface\\AddOns\\… instead of
\\addons\\…) to match every other path in the file.

Leatrix_Plus.lua

@@ -11384,7 +11384,7 @@ function LeaPlusLC:Player()
         local miniButton = LibStub("LibDataBroker-1.1"):NewDataObject("Leatrix_Plus", {
             type = "data source",
             text = "Leatrix Plus",
-            icon = "Interface\\addons\\Leatrix_Plus\\assets\\minimapicon.tga",
+            icon = "Interface\\AddOns\\Leatrix_Plus\\assets\\minimapicon.blp",
             OnClick = function(self, btn)
                 MiniBtnClickFunc(btn)
             end,