LibJS+LibWeb: Convert string view PrimitiveString instances to String

First, this adds an overload of PrimitiveString::create for StringView.
This overload will throw an OOM completion if creating a String fails.
This is not only a bit more convenient, but it also ensures at compile
time that all PrimitiveString::create(string_view) invocations will be
handled as String and OOM-aware.

Next, this wraps all invocations to PrimitiveString::create(string_view)
with MUST_OR_THROW_OOM.

A small PrimitiveString::create(DeprecatedFlyString) overload also had
to be added to disambiguate between the StringView and DeprecatedString
overloads.

Userland/Libraries/LibJS/Runtime/Intl/DisplayNames.cpp

@@ -166,7 +166,7 @@ ThrowCompletionOr<Value> canonical_code_for_display_names(VM& vm, DisplayNames::
             return vm.throw_completion<RangeError>(ErrorType::OptionIsNotValidValue, code, "dateTimeField"sv);
 
         // b. Return code.
-        return PrimitiveString::create(vm, code);
+        return MUST_OR_THROW_OOM(PrimitiveString::create(vm, code));
     }
 
     // 6. Assert: type is "currency".