improve(terminal): pass terminal capability to server in advance

[ericwq]

for example:

client should check the CSI u capability in advance and pass it to aprilsh server. for CSI u query, server can response to terminal application asap.

if the terminal emulator doesn't support CSI u, the server can response to terminal application directly.
if the terminal emulator does support CSI u, query, set, push ,pop request can be responded on the server side immediately, while set, push, pop request need to reach the client side to change the keyboard encoding.

[ericwq]

CSI u is passed to server for using