feat(css): add assignment textobjects (#544)

Author: pockata

queries/css/textobjects.scm

@@ -3,3 +3,14 @@
   (float_value)
   (color_value)
 ] @number.inner
+
+(declaration
+  (property_name) @assignment.lhs
+  . ":" . (_) @_start (_)? @_end . ";"
+  (#make-range! "assignment.inner" @_start @_end)
+  (#make-range! "assignment.rhs" @_start @_end)
+) @assignment.outer
+
+(declaration
+  (property_name) @assignment.inner
+)