Improve CSS syntax highlighting

[chbk]

Release Notes:

• Improved CSS syntax highlighting

Zed 0.174.6	With this PR

• |: operator
• and, or, not, only: operator -> keyword.operator, as defined in other languages
• id_name, class_name: property -> selector, not a property name. CSS reference
• namespace_name: property -> namespace, not a property name
• property_name: constant -> property, like feature_name already defined
• (keyword_query): property, similar to feature_name. CSS reference
• keyword_query: constant.builtin, CSS reference
• plain_value, keyframes_name: constant.builtin, CSS reference
• unit: type -> type.unit, Atom and VS Code also have a unit scope for this. CSS reference

@media (keyword_query) and keyword_query {}
@supports (feature_name: plain_value) {}
@namespace namespace_name url("string");
namespace_name|tag_name {}
@keyframes keyframes_name {
  to {
    top: 200unit;
    color: #c01045;
  }
}
tag_name::before,
#id_name:nth-child(even),
.class_name[attribute_name=plain_value] {
  property_name: 2em 1.2em;
  --variable: rgb(250, 0, 0);
  color: var(--variable);
  animation: keyframes_name 5s plain_value;
}