std.ascii: remove LUT and deprecations

[wooster0]

I wrote this after #12448 got merged but decided to wait for 0.10.0 to be released before pulling it. Now I've decided to pull it a bit earlier since 0.10.0 is just about to be released, anyway (and in case someone else would accidentally start working on the same thing or something).

This should be merged after 0.10.0 and removes all deprecations, updates the codebase, does some other cleanups etc., and also removes the LUT (Look-Up Table): this was already discussed quite a bit in #11629 (see https://github.com/ziglang/zig/pull/11629#issuecomment-1213641429 etc.) and I've also discussed this with @topolarity in more detail after that, but basically the reason is that the LUT made us depend on cache performance. It also reduces binary size. See also the commit's description for more detail.

Removing both the deprecations and the LUT at the same time is a very convenient timing, by the way. It shouldn't make review that much harder, I hope.

[wooster0]

Well, I suspect the CI failure might be related and after double-checking a bunch of stuff I'm not yet sure what could be causing it, but maybe it will resolve itself with a commit later.

[wooster0]

Well, I'm not sure what's causing these CI failures. If I look at https://cloud.drone.io/ziglang/zig/22186/1/3 then it seems I should be able to reproduce locally using zig build test-behavior -Dskip-non-native --zig-lib-dir lib on my branch right? Well, if I run that, it all passes... However the CI also rebuilds the compiler. Unfortunately I have trouble building the compiler (if it has to include LLVM at least) so at least for now I won't be able to reproduce this locally. But this PR exclusively makes changes to lib/std so I shouldn't have to compile the compiler. Is this some kind of miscompilation? I'm going to try another rebase... which did not solve it.