Changes

ctf.core: Initial field class implementation

Implement the fixed unsigned integer field class and
create new structures from a trace fragment. Currently
the preamble fragment is not parsed as the code would
only deal with user attributes and extensions
which have not been implemented yet. Additionally,
field classes that are not Json Objects (field class
aliases) have not yet been handled.

Change-Id: Icfc28b0fbee9c037ebd8ca58a24da1eb389d2018
Signed-off-by: Sehr Moosabhoy <sehr.moosabhoy@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/c/tracecompass/org.eclipse.tracecompass/+/202815
Tested-by: Trace Compass Bot <tracecompass-bot@eclipse.org>
Tested-by: Marco Miller <marco.miller@ericsson.com>
Reviewed-by: Marco Miller <marco.miller@ericsson.com>