Only two fields of AVTextFormatSection are ever modified:
entries_to_show and show_all_entries (they are only used
by ffprobe; the graph printing code always prints everything).
These fields do not belong into AVTextFormatSection, they are
more ffprobe-internal (and if the graph printing code ever
made use of them, these fields could very well be
per GraphPrintContext).
This commit therefore moves them out of AVTextFormatSection
and adds a callback to AVTextFormatContext to decide which
elements to discard. This also allows to make the AVTextFormatSections
const.
This also fixes a race when initializing the sections
for graphprint.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>