It replaces Send button when the user is editing an inline bot
query. First cancel clears the inline bot request, second one
clears the field entirely. Escape key acts the same as cancel.
All errors that lead to MTP request resending by default
error handler now can be handled differently. For example
inline bot requests are not being resent on 5XX error codes.
+ extensive use of auto keyword in MTP types handling.
John Preston