libjob: support emoji jobid encoding

Problem: libjob does not support encoding flux_jobid_t to emoji.

Add an "emoji" encoding that uses FLUX_STRING_EMOJI to encode
flux_jobid_t as a string of emoji using the basemoji implementation.

Author: grondo

src/common/libjob/id.c

@@ -88,6 +88,8 @@ int flux_job_id_encode (flux_jobid_t id,
         t = FLUID_STRING_MNEMONIC;
     else if (strcasecmp (type, "f58") == 0)
         t = FLUID_STRING_F58;
+    else if (strcasecmp (type, "emoji") == 0)
+        t = FLUID_STRING_EMOJI;
     else {
         /*  Return EPROTO for invalid type to differentiate from
          *   other invalid arguments.