gdb: gst-print add more pad and element information

gdb: gst-print add more pad and element information

For elements, this adds all child elements, the state and base/start time:

(gdb) gst-print pipeline
0x5555556ebd20 "pipeline0"
GstPipeline(pipeline0) {
    children:
      fakesink0
      queue0
      videotestsrc0
    state: PLAYING
    base_time: +2:54:36.892581150
    start_time: 0:00:00.000000000
}

For pads, this adds the peer pads and the current task state and the
offset (if not zero):

(gdb) gst-print pad
SrcGhostPad(src, push) {
  events:
    [...]
  peer: vaapisink0:sink
  inner peer: scale:src
}

(gdb) gst-print pad
SrcPad(src, push) {
  events:
    [...]
  peer: queue0:sink
  task: STARTED
  offset: 30000000 [+0:00:00.030000000]
}