ui: mostly cocoa fixes

# gpg: Signature made Thu 11 Mar 2021 12:33:51 GMT
# gpg:                using RSA key A0328CFFB93A17A79901FE7D4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/ui-20210311-pull-request:
  ui/cocoa: Fix mouse association state
  ui/cocoa: Mark variables static
  ui/cocoa: Clear modifiers whenever possible
  ui/cocoa: Do not rely on the first argument
  ui/cocoa: Show QEMU icon in the about window
  docs: Fix removal text of -show-cursor
  ui/cocoa: Use kCGColorSpaceSRGB
  ui/gtk: Remove NULL checks in gd_switch

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>