Rename enum values used for HTTP/3 and QPACK RFC defined codes. First
uses a prefix H3_ERR_* which serves as identifier between them. Also
separate QPACK values in a new dedicated enum qpack_err. This is deemed
cleaner.
Previously, statistics were simply defined as a list of name_desc, as
for example "stat_cols_px" for proxy stats. No notion of type was fixed
for each stat definition. This correspondance was done individually
inside stats_fill_*_line() functions. This renders the process to
define new statistics tedious.
Implement a more expressive stat definition method via a new API. A new
type "struct stat_col" for stat column to replace name_desc usage is
defined. It contains a field to store the stat nature and format. A
<cap> field is also defined to be able to define a proxy stat only for
certain type of objects.
This new type is also further extended to include counter offsets. This
allows to define a method to automatically generate a stat value field
from a "struct stat_col". This will be the subject of a future commit.
New type "struct stat_col" is fully compatible full name_desc. This
allows to gradually convert stats definition. The focus will be first
for proxies counters to implement statistics preservation on reload.
It is now possible to selectively retrieve extra counters from stats
modules. H1, H2, QUIC and H3 fill_stats() callback functions are updated to
return a specific counter.
Add ->inc_err_cnt new callback to qcc_app_ops struct which can
be called from xprt to increment the application level error code counters.
It take the application context as first parameter to be generic and support
new QUIC applications to come.
Add h3_stats.c module with counters for all the frame types and error codes.
