1) Move a bunch of std::map's to std::unordered_map to get constant-time
look-ups
2) Lengthen progress-reporting intervals to spend more time doing work
and less time talking about it
3) Reverse order of SHAPE_LINE_CHAINs in thermal intersection checks to
make (much) better use of bbox caches
4) Don't re-generate bboxes we already have
5) Fix some autos that weren't by reference (and were therefore copying
large datasets)
6) Rename delta progressDelta so it's easier to search for in future
7) Get rid of a few more autos (because I don't like them)
8) Pass large items to lambdas by reference
Fixes https://gitlab.com/kicad/code/kicad/issues/12130
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
Jeff Young
Seth Hillbrand
Mark Roszko