tmf: make CallstackProvider entry and exit return TmfStates

tmf: make CallstackProvider entry and exit return TmfStates

This allows certain callstacks to return simpler long or int
states instead of a string. Expect SIGNIFICANT space savings.

In an example application, ls was traced (coreutils 8
with -finstrument-functions)

For a 149 mb trace with no lost events.

State system size
before:
233 mb
after:
25mb

Total time for trace compass fullscreen (1920x1080)

read the trace and build the state systems:
before:
61.5 sec
after:
44.0 sec

average seek time (100ms window, 10 random locations)
before:
1.2 sec
after:
0.6 s

Change-Id: Ic868829296d92d854cda7b78784b6ee3be4d5a51
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/70719
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Hudson CI