LibWeb/HTML: Implement <input> element valueAsNumber for 'month'

Author: https://github.com/shannonbooth
Commit: 6c2ad49ed2
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3485
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/gmta
Reviewed-by: https://github.com/trflynn89

Tests/LibWeb/Text/expected/HTML/HTMLInputElement-valueAsNumber.txt

@@ -32,7 +32,7 @@ url threw exception: InvalidStateError: valueAsNumber: Invalid input type used
 email threw exception: InvalidStateError: valueAsNumber: Invalid input type used
 password threw exception: InvalidStateError: valueAsNumber: Invalid input type used
 date did not throw: NaN
-month did not throw: NaN
+month did not throw: 100
 week did not throw: NaN
 time did not throw: NaN
 datetime-local did not throw: NaN