dumpsys: add --pid option

We can't change the output format of dumpsys since too many places rely
on it, so introducing a separate option to dump the PID of a service.

Fixes: 141187318
Test: dumpsys_test, bugreport, also:
$ adb shell dumpsys --pid
...
-------------------------------------------------------------------------------
DUMP OF SERVICE package_native:
1165
--------- 0.001s was the duration of dumpsys package_native, ending at: 2019-10-08 20:35:32
...
(dumps pids of all services)

or with specific service name only:
$ dumpsys --pid package_native
1165

Change-Id: Iaa2478568245ca7d10d2e3f8ebafe43d2d26df2c