theme: use max_toggled_hover.xbm

...and treat max_hover_toggled.xbm as an alternative name supported for
compatibility reasons.

Use the following button filename schema: "BUTTON [TOGGLED] [STATE]"
with the words separted by underscore and with the following meaning:
  - BUTTON can be one of 'max', 'iconify', 'close', 'menu'
  - TOGGLED is either 'toggled' or nothing
  - STATE is 'hover' or nothing.

This is consistent with the openbox.org wiki and it is believed that this
is how the vast majority of extant openbox themes out there are written.

But please be aware that it is actually different to vanilla Openbox which
uses: "BUTTON [STATE] [TOGGLED]" following a commit in 2014 which broke
themes and led to some distros patching Openbox:
35e92e4c2a

Arch Linux and Debian patch Openbox to keep the old syntax (the one that
this commit aligns us with).
https://gitlab.archlinux.org/archlinux/packaging/packages/openbox/-/blob/main/debian-887908.patch?ref_type=heads

docs/labwc-theme.5.scd

@@ -206,12 +206,16 @@ over the button in question:
 - iconify_hover.xbm
 - close_hover.xbm
 - menu_hover.xbm
-- max_hover_toggled.xbm
+- max_toggled_hover.xbm
 
 One advantage of xbm buttons over other formats is that they change color based
 on the theme. Other formats use the suffices "-active" and "-inactive" to align
 with the respective titlebar colors. For example: "close-active.png"
 
+For compatibility reasons, the following alternative names are supported:
+
+- max_hover_toggled.xbm for max_toggled_hover.xbm
+
 # DEFINITIONS
 
 The handle is the window edge decoration at the bottom of the window.