`ctf` plugin: metadata: use BT_COMP_LOG*() instead of BT_LOG*()

`ctf` plugin: metadata: use BT_COMP_LOG*() instead of BT_LOG*()

Because we need to pass around the log level and the self component
pointer at several places within the files of this directory, this patch
adds a new internal `struct meta_log_config` which contains both and can
be passed as a single parameter and contained as a single member. It is
not meant to be known by anything calling the functions from files
outside this directory.

The generated parser and lexer can't use the BT_COMP_LOG*() macros
because they lack contextual data to access the self component pointer,
so they are left as is.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Ifa95256e7931416b890e8da0bb7c2552f396a8d2
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1499