unity_screen_service: implement com.lomiri.Repowerd.listSysRequests()

implement com.lomiri.Repowerd.listSysRequests() as noted in https://gitlab.com/ubports/development/core/repowerd/-/blob/8a6500d5cca833f191cd9fadeb2056034ce8a5fd/data/dbus-configs/com.lomiri.Repowerd.conf#L44

Helps with debugging, possibly also monitoring and automations on external components

also include repowerd-cli dumper

phablet@ubuntu-phablet:~/repowerd_listSysRequests$ repowerd-cli listsysrequests 
Listing currently active sys requests (suspend block request):
sender: :1.1365 | sender pid: 44774 | id/cookie: 7 | name: test 2
sender: :1.1365 | sender pid: 44774 | id/cookie: 6 | name: test 1
sender: :1.1365 | sender pid: 44774 | id/cookie: 5 | name: test 0
sender: :1.1362 | sender pid: 44767 | id/cookie: 4 | name: test 2
sender: :1.1362 | sender pid: 44767 | id/cookie: 3 | name: test 1
sender: :1.1362 | sender pid: 44767 | id/cookie: 2 | name: test 0

Listing currently active keep display on requests:
sender: :1.1365 | sender pid: 44774 | id/cookie: 6
sender: :1.1365 | sender pid: 44774 | id/cookie: 5
sender: :1.1365 | sender pid: 44774 | id/cookie: 4
sender: :1.1362 | sender pid: 44767 | id/cookie: 3
sender: :1.1362 | sender pid: 44767 | id/cookie: 2
sender: :1.1362 | sender pid: 44767 | id/cookie: 1

Listing currently active notification requests:
sender: :1.1365 | sender pid: 44774 | reason: 4
sender: :1.1365 | sender pid: 44774 | reason: 4
sender: :1.1365 | sender pid: 44774 | reason: 4
sender: :1.1362 | sender pid: 44767 | reason: 4
sender: :1.1362 | sender pid: 44767 | reason: 4
sender: :1.1362 | sender pid: 44767 | reason: 4