package/webkitgtk: security bump to 2.34.6

Update to a new major release which brings in improvements, a number of
new features, and security fixes. Release notes:

  https://webkitgtk.org/2021/09/22/webkitgtk2.34.0-released.html
  https://webkitgtk.org/2021/10/21/webkitgtk2.34.1-released.html
  https://webkitgtk.org/2021/11/24/webkitgtk2.34.2-released.html
  https://webkitgtk.org/2021/12/20/webkitgtk2.34.3-released.html
  https://webkitgtk.org/2022/01/21/webkitgtk2.34.4-released.html
  https://webkitgtk.org/2022/02/09/webkitgtk2.34.5-released.html
  https://webkitgtk.org/2022/02/17/webkitgtk2.34.6-released.html

Security advisories:

  https://webkitgtk.org/security/WSA-2021-0007.html
  https://webkitgtk.org/security/WSA-2022-0001.html
  https://webkitgtk.org/security/WSA-2022-0002.html
  https://webkitgtk.org/security/WSA-2022-0003.html



Some of the new features require additional dependencies: HTTP/2
requires libsoup3, which is not yet packaged in Buildroot, and
disabled at the moment (with -DUSE_SOUP2=ON, to keep using libsoup2);
and the color management support needs LCMS2 (which will be enabled
in a follow-up patch.)

Options SILENCE_CROSS_COMPILATION_NOTICES and ENABLE_GRAPHICS_CONTEXT_GL
do not exist anymore, and their usage is dropped.

Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>