FIX: Correctly report command keypress on mac for Tk + Gtk

Tk and Gtk reported "super" when "command" was pressed, while qt and
macosx reported "cmd". Make all backends consistent by reporting
"cmd" in all of them.

@co-authored-by: Antony Lee <[email protected]>

Author: greglucas

lib/matplotlib/backends/_backend_tk.py

@@ -354,7 +354,7 @@ def _mpl_modifiers(event, *, exclude=None):
             ("ctrl", 1 << 2, "control"),
             ("alt", 1 << 4, "alt"),
             ("shift", 1 << 0, "shift"),
-            ("super", 1 << 3, "super"),
+            ("cmd", 1 << 3, "cmd"),
         ] if sys.platform == "darwin" else [
             ("ctrl", 1 << 2, "control"),
             ("alt", 1 << 3, "alt"),

lib/matplotlib/cbook.py

@@ -2169,6 +2169,9 @@ def _unikey_or_keysym_to_mplkey(unikey, keysym):
         key = key.replace("page_", "page")
     if key.endswith(("_l", "_r")):  # alt_l, ctrl_l, shift_l.
         key = key[:-2]
+    if sys.platform == "darwin" and key == "meta":
+        # meta should be reported as command on mac
+        key = "cmd"
     key = {
         "return": "enter",
         "prior": "pageup",  # Used by tk.