- Added functional test to verify `asp-*` attributes on form taghelpers work as expected.
- Added a unit test to validate `FormTagHelper` behaves as expected.
- Moved `Method == "get"` checks into appropriate code paths. These include the one where a user specifies an empty or non-existent `action` attribute and where a user doesn't utilize any `asp-*` attributes. In the later, we default `Method` to `"get"` if it's not provided.
#6006
