common: implement bt_common_g_string_append and bt_common_g_string_append_c

common: implement bt_common_g_string_append and bt_common_g_string_append_c

Implement inline versions of g_string_append and
g_string_append_c. Since those calls are performed very often within
sink.text.pretty, it is relevant for pretty-printing speed.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: Ib1069c7d21c6e707f75d839f333f034a50e2a43e
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1515
CI-Build: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>