MINOR: mux_quic/h3: report termination events at connection level

MINOR: mux_quic/h3: report termination events at connection level

Implement termination event log in QUIC MUX layer at the connection
level. The objective is to reuse similar codes already used on H2.

Most of the error values are reported via qcc_set_error() which have now
an extra argument to specify the term event code. This is in particular
used in H3 application protocol code.

Also, qmux_ctl() now implements MUX_CTL_TEVTS to report the current
connection termination code to the upper layer. Callback qmux_sctl()
display the connection term event code on MUX_SCTL_DBG_STR.