feat(keybindings): add cmd+shift+p and cmd+/ keybindings from VSCode

Makes cmd+shift+p open the command palette and cmd+/ toggle comments, as
they do in VSCode.

This should ease my recent usage of Cursor/VSCode alongside Emacs, as
certain keybindings I have in Emacs cannot be setup in VSCode to work in
all contexts. Hence I've had to get used to cmd+shift+p instead of C-x
C-m, as the later does not want to play ball when a terminal is active
in VSCode.

modules/core/siren-global-keybindings.el

@@ -9,6 +9,7 @@
 (siren-general-define-key
  ;; Enable alternative to M-x.
  "C-x C-m" 'execute-extended-command
+ "s-P" 'execute-extended-command
 
  ;; Enable dabbrev-expand via custom keybinding.
  "C-x M-/" 'dabbrev-expand