LibWeb: Add SVG-presentation-attribute-parsing mode to CSS parser

When parsing these, <number> is allowed anywhere that would usually
allow a <length>, <length-percentage>, or <angle>. The spec is not
clear on exactly how this should work
(see https://github.com/w3c/svgwg/issues/792 ) so I'm using some
artistic license until things are clearer:
- If we expected a <length>, treat the <number> as pixels.
- If we expected an <angle>, treat the <number> as degrees.
- Only allow direct <number> tokens, not calc() or other functions.

From what I can tell this is what the spec *intended* but I may be very
wrong. In any case, telling the ParsingContext whether we're parsing
one of these attributes is a cleaner approach and more correct than
temporarily enabling quirks mode, which we did previously.

Userland/Libraries/LibWeb/CSS/Parser/ParsingContext.cpp

@@ -13,29 +13,33 @@
 
 namespace Web::CSS::Parser {
 
-ParsingContext::ParsingContext(JS::Realm& realm)
+ParsingContext::ParsingContext(JS::Realm& realm, Mode mode)
     : m_realm(realm)
+    , m_mode(mode)
 {
 }
 
-ParsingContext::ParsingContext(DOM::Document const& document, AK::URL url)
+ParsingContext::ParsingContext(DOM::Document const& document, AK::URL url, Mode mode)
     : m_realm(const_cast<JS::Realm&>(document.realm()))
     , m_document(&document)
     , m_url(move(url))
+    , m_mode(mode)
 {
 }
 
-ParsingContext::ParsingContext(DOM::Document const& document)
+ParsingContext::ParsingContext(DOM::Document const& document, Mode mode)
     : m_realm(const_cast<JS::Realm&>(document.realm()))
     , m_document(&document)
     , m_url(document.url())
+    , m_mode(mode)
 {
 }
 
-ParsingContext::ParsingContext(DOM::ParentNode& parent_node)
+ParsingContext::ParsingContext(DOM::ParentNode& parent_node, Mode mode)
     : m_realm(parent_node.realm())
     , m_document(&parent_node.document())
     , m_url(parent_node.document().url())
+    , m_mode(mode)
 {
 }