Improve treesit settings for css-ts-mode (bug#73404)

Improve treesit settings for css-ts-mode (bug#73404)

* lisp/textmodes/css-mode.el (css--treesit-settings): Add
"@supports" and '(at_keyword)' to 'keyword', 'keyframe_block' to
'selector', 'keyframes_name' to 'query'.
(css--treesit-defun-name): Support "keyframe_block",
"keyframes_statement" and "supports_statement" as well.
(css--treesit-simple-imenu-settings): Add "keyframes_statement",
"keyframe_block", "supports_statement".
(css--treesit-defun-type-regexp): Add "keyframe_block".
(css-ts-mode): Add 'treesit-thing-settings'.

(cherry picked from commit a5e82110b087f05d50a9d628e70009ce33c33bc2)