MINOR: mux-quic: add function for ALPN to app-ops conversion

MINOR: mux-quic: add function for ALPN to app-ops conversion

Extract the conversion from ALPN to qcc_app_ops type from quic_conn
source file into QUIC MUX. The newly created function is named
quic_alpn_to_app_ops(). This will serve as a central point to identify
which ALPNs are currently supported in our QUIC stack.

This patch is purely a small refactoring. It will be useful for the next
one which rework MUX app-ops layer init. The current cleanup allows
notably to remove H3/hq-interop headers from quic_conn source file.