Add printf format for GTID

We use %u-%u-%llu to format GTID fields in my_/snprintf.
But GTIDs use fixed integer sizes since merge, while %u and %llu technically varies by platform.

We should define a platform-agnostic printf format and apply it throughout the codebase.
It could be…

… a macro that complements PARAM_GTID – naming candidates are:

• Standard C/C++-style: PRIuGTID
• InnoBase-style: GTIDPF

(I prefer the Standard style because we should phase out InnoBase’s extra typedefs in favor of standardized ones (MDEV-35460).)

… a function – a method of rpl_gtid?

… a custom my_snprintf format extension – %pG?

This implementation is the only one of the three that sql/share/errmsg-utf8.txt gets to utilize.