perfetto_cmd: overhaul --query

This solves two problems:
1. The output of --query has become too verbose over time
   and human unfriendly. --query has always been meant as
   an aid to humans to tell what's going on in the service.
2. Add an option to list the names of the ongoing tracing
   sessions. We tend to need it frequently in droidfood.

Example output:
```
Not meant for machine consumption. Use --query-raw for scripts.

Service: Perfetto v23.0-4bf9e6896 (4bf9e6896e9fc4902756927ec9ff225e04a755c7)
Tracing sessions: 1 (started: 1)


PRODUCER PROCESSES CONNECTED:

ID         PID        UID        NAME                             SDK
==         ===        ===        ====                             ===
1          3471       0          perfetto.traced_probes           Perfetto v23.0-4bf9e6896

DATA SOURCES REGISTERED:

NAME                                     PRODUCER                     DETAILS
===                                      ========                     ========
android.log                              perfetto.traced_probes (1)
android.packages_list                    perfetto.traced_probes (1)
android.polled_state                     perfetto.traced_probes (1)
android.power                            perfetto.traced_probes (1)
linux.ftrace                             perfetto.traced_probes (1)
linux.inode_file_map                     perfetto.traced_probes (1)
linux.process_stats                      perfetto.traced_probes (1)
linux.sys_stats                          perfetto.traced_probes (1)
linux.sysfs_power                        perfetto.traced_probes (1)
linux.system_info                        perfetto.traced_probes (1)
perfetto.metatrace                       perfetto.traced_probes (1)


TRACING SESSIONS:

ID      UID     STATE      NAME         BUF (#) KB   DUR (s)   #DS  STARTED
===     ===     =====      ====         ==========   =======   ===  =======
8       0       STARTED    aot_test     (1) 65536    10        4    01:08:08

```


Change-Id: I16785bcb701a3e6d006cd9aae5262ca8ed1442f6
diff --git a/CHANGELOG b/CHANGELOG
index 8dbe728..9b62dc9 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,7 @@
 Unreleased:
   Tracing service and probes:
-    *
+    * Changed output format of perfetto --query. Made the output more compact
+      and added a summary of ongoing tracing sessions for the caller UID.
   Trace Processor:
     *
   UI: