Fix: CTF writer: make library have its own public `types.h`

Fix: CTF writer: make library have its own public `types.h`

This was overlooked when segregating the CTF writer library from the
Babeltrace library: CTF writer needs its own `bt_ctf_bool` type with its
own `BT_CTF_TRUE` and `BT_CTF_FALSE` definitions.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I4e6d0b2d0956479a554cc8358d646fc1676873f6
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1667
Tested-by: jenkins <jenkins@lttng.org>