LibWeb/CSS: Integrate ParsingContext into the Parser

This is not really a context, but more of a set of parameters for
creating a Parser. So, treat it as such: Rename it to ParsingParams,
and store its values and methods directly in the Parser instead of
keeping the ParsingContext around.

This has a nice side-effect of not including DOM/Document.h everywhere
that needs a Parser.

Libraries/LibWeb/IntersectionObserver/IntersectionObserver.cpp

@@ -319,7 +319,7 @@ void IntersectionObserver::queue_entry(Badge<DOM::Document>, GC::Ref<Intersectio
 Optional<Vector<CSS::LengthPercentage>> IntersectionObserver::parse_a_margin(JS::Realm& realm, String margin_string)
 {
     // 1. Parse a list of component values marginString, storing the result as tokens.
-    auto tokens = CSS::Parser::Parser::create(CSS::Parser::ParsingContext { realm }, margin_string).parse_as_list_of_component_values();
+    auto tokens = CSS::Parser::Parser::create(CSS::Parser::ParsingParams { realm }, margin_string).parse_as_list_of_component_values();
 
     // 2. Remove all whitespace tokens from tokens.
     tokens.remove_all_matching([](auto componentValue) { return componentValue.is(CSS::Parser::Token::Type::Whitespace); });