Everywhere: Rename to_{string => deprecated_string}() where applicable

This will make it easier to support both string types at the same time
while we convert code, and tracking down remaining uses.

One big exception is Value::to_string() in LibJS, where the name is
dictated by the ToString AO.

Userland/Libraries/LibWeb/Fetch/Body.cpp

@@ -162,7 +162,7 @@ JS::NonnullGCPtr<JS::Promise> consume_body(JS::Realm& realm, BodyMixin const& ob
     // 4. Let steps be to return the result of package data with the first argument given, type, and object’s MIME type.
     auto steps = [&realm, &object, type](JS::Value value) -> WebIDL::ExceptionOr<JS::Value> {
         VERIFY(value.is_string());
-        auto bytes = TRY_OR_RETURN_OOM(realm, ByteBuffer::copy(value.as_string().string().bytes()));
+        auto bytes = TRY_OR_RETURN_OOM(realm, ByteBuffer::copy(value.as_string().deprecated_string().bytes()));
         return package_data(realm, move(bytes), type, object.mime_type_impl());
     };
 

Userland/Libraries/LibWeb/Fetch/BodyInit.cpp

@@ -87,7 +87,7 @@ WebIDL::ExceptionOr<Infrastructure::BodyWithType> extract_body(JS::Realm& realm,
         },
         [&](JS::Handle<URL::URLSearchParams> const& url_search_params) -> WebIDL::ExceptionOr<void> {
             // Set source to the result of running the application/x-www-form-urlencoded serializer with object’s list.
-            source = url_search_params->to_string().to_byte_buffer();
+            source = url_search_params->to_deprecated_string().to_byte_buffer();
             // Set type to `application/x-www-form-urlencoded;charset=UTF-8`.
             type = TRY_OR_RETURN_OOM(realm, ByteBuffer::copy("application/x-www-form-urlencoded;charset=UTF-8"sv.bytes()));
             return {};

Userland/Libraries/LibWeb/Fetch/Infrastructure/HTTP.cpp

@@ -69,7 +69,7 @@ DeprecatedString collect_an_http_quoted_string(GenericLexer& lexer, HttpQuotedSt
 
     // 6. If the extract-value flag is set, then return value.
     if (extract_value == HttpQuotedStringExtractValue::Yes)
-        return value.to_string();
+        return value.to_deprecated_string();
 
     // 7. Return the code points from positionStart to position, inclusive, within input.
     auto position = lexer.tell();