Make application transparency opt-in (#14253)

* Make application transparency opt-in

* Use the transparency helper for Kanagawa

* Address transparency review findings

* Toggle transparency for opaque windows too

default/hypr/apps/pip.lua

@@ -1,24 +1,20 @@
 -- Picture-in-picture overlays.
 o.window({ title = "(Picture.?in.?[Pp]icture)" }, { tag = "+pip" })
 o.window({ tag = "pip" }, {
-  tag = "-default-opacity",
   float = true,
   pin = true,
   size = { 600, 338 },
   keep_aspect_ratio = true,
   border_size = 0,
-  opacity = "1 1",
   move = { "(monitor_w-window_w-40)", "(monitor_h*0.04)" },
 })
 
 -- Google Meet PiP uses the meeting title instead of "Picture-in-Picture".
 o.window({ tag = "chromium-based-browser", title = "^Meet - .+" }, {
-  tag = "-default-opacity",
   float = true,
   pin = true,
   size = { 600, 338 },
   keep_aspect_ratio = true,
   border_size = 0,
-  opacity = "1 1",
   move = { "(monitor_w-window_w-40)", "(monitor_h-window_h-40)" },
 })