WM: support the "Hyper" modifier key on Linux

Add support for a 5th modifier key called "hyper",
this is a modifier supported on Wayland & X11 although
other platforms could support an additional modifier too.

Both GNOME and KDE can map CapsLock to Hyper.
Other compositors can use the XKB_DEFAULT_OPTIONS environment variable.

This allows users to have an additional modifier for their own use
that doesn't conflict with other keys.

Ref !136340

scripts/modules/bl_keymap_utils/io.py

@@ -47,7 +47,7 @@ def kmi_args_as_data(kmi):
     if kmi.any:
         s.append("\"any\": True")
     else:
-        for attr in ("shift", "ctrl", "alt", "oskey"):
+        for attr in ("shift", "ctrl", "alt", "oskey", "hyper"):
             if mod := getattr(kmi, attr):
                 s.append(f"\"{attr:s}\": " + ("-1" if mod == -1 else "True"))
     if (mod := kmi.key_modifier) and (mod != 'NONE'):

scripts/modules/bl_keymap_utils/keymap_from_toolbar.py

@@ -24,6 +24,7 @@ def generate(context, space_type, *, use_fallback_keys=True, use_reset=True):
                 ("ctrl", False),
                 ("alt", False),
                 ("oskey", False),
+                ("hyper", False),
                 ("key_modifier", 'NONE'),
         ):
             val = getattr(kmi, attr)

scripts/modules/rna_keymap_ui.py

@@ -201,6 +201,11 @@ def draw_kmi(display_keymaps, kc, km, kmi, layout, level):
             subrow.prop(kmi, "alt_ui", toggle=True)
             subrow.prop(kmi, "oskey_ui", text="Cmd", toggle=True)
 
+            # On systems that don't support Hyper, only show if it's enabled.
+            # Otherwise the user may have a key binding that doesn't work and can't be changed.
+            if _platform_supports_hyper_key() or kmi.hyper == 1:
+                subrow.prop(kmi, "hyper_ui", text="Hyper", toggle=True)
+
             subrow.prop(kmi, "key_modifier", text="", event=True)
 
         # Operator properties
@@ -218,6 +223,16 @@ _EVENT_TYPES = set()
 _EVENT_TYPE_MAP = {}
 _EVENT_TYPE_MAP_EXTRA = {}
 
+_HAS_HYPER_KEY = None
+
+
+def _platform_supports_hyper_key():
+    global _HAS_HYPER_KEY
+    if _HAS_HYPER_KEY is None:
+        from _bpy import _ghost_backend
+        _HAS_HYPER_KEY = _ghost_backend() in {'WAYLAND', 'X11'}
+    return _HAS_HYPER_KEY
+
 
 def draw_filtered(display_keymaps, filter_type, filter_text, layout):
 
@@ -259,6 +274,7 @@ def draw_filtered(display_keymaps, filter_type, filter_text, layout):
             "alt": "alt",
             "shift": "shift",
             "oskey": "oskey",
+            "hyper": "hyper",
             "any": "any",
 
             # macOS specific modifiers names