Move charconv tables

[AlexGuteniev]

Resolve #172
Resolve #2347

[StephanTLavavej]

Thanks, this looks great! I've carefully verified that all of the code movement is preserving the tables and changing only necessary things. I've also verified that mixing TUs calling to_chars() that have been compiled with main and this PR results in successful linking, so I don't believe that we need to rename the individual tables (renaming the specialized struct is good and minimally invasive).

I've also verified that the generators continue to compile. They don't generate exactly what's in the headers now, but the transformations are obvious, and I would definitely prefer to avoid mixing the code movement here with any nontrivial updates to the generators.

I will validate and push changes for the minor issues I noticed.

[StephanTLavavej]

I'm speculatively mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

I've had to push an additional commit to work around VSO-1579484 "Standard Library Header Units: charconv refactoring + topo sort = error LNK2019: unresolved external symbol".

[StephanTLavavej]

I've pushed changes to remove the /* static */ comments (which caused the float tables to reflow). We have a few occurrences of comments like /* = 0 */ which are questionably useful, but this case is different (the definitions couldn't be for anything other than static data members).

I've also pushed a workaround change, suggested by @cdacamar, which avoids the need to modify the <charconv> usage (although the workaround itself is somewhat more verbose). If we ever need to do this elsewhere before the compiler bug is fixed, the one that doesn't require modifying every usage is better.

[StephanTLavavej]

Thanks for this significant throughput improvement - it should substantially reduce the size of the Standard Library Header Units and Modules too! 😻 🚀 🎉