Display multibyte e-expression headers

[zslayton]

Currently, inspect assumes all e-expressions will have a one-byte header: https://github.com/amazon-ion/ion-cli/blob/03a3fc87edce093b3c00415eec6dccfc5aec99be/src/bin/ion/commands/inspect.rs#L458-L466

However, is only the case for invocations of user macros with an ID lower than 64. Invocations of system macros are two bytes (0xEE 0x__), and invocations of macros with IDs >= 64 are at least two bytes.