This one for symbol <-> footprint. (Original was for
lib footprint <-> board footprint.)
Also fixes a major bug in DRC where we bail out of parity
checking if DRCE_MISSING_FOOTPRINT is set to ignore (or
overflows).
Fixes https://gitlab.com/kicad/code/kicad/-/issues/16671
Threaded DRC access will write to this string, re-allocating the memory
without any synchronization between threads using the string. Comment
adding this listed performance as a reason for using shared strings.
Measured performance does not seem noticeably different in either case,
even with high-error count boards. If there is a case where the
performance is limiting, we can replace these wxStrings with
std::wstring and utilize fmt
Fixes https://gitlab.com/kicad/code/kicad/issues/9888