Merge: typing: get_method refactoring

Split the get_method to three different entry points. These new entry points make it possible to adapt the treatment to the actual context. This avoids creating callsites manually and in the same time do the verification if the researched method exist (display an error if not exist)

Signed-off-by: Florian Deljarry <deljarry.florian@gmail.com>

Pull-Request: #2760
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Jean Privat <jean@pryen.org>