v.scanner: use table lookups for very frequently done character checks

[spytheman]

This has only the lookup changes from #21545 .
The substr_unsafe commit, turned out to be a problem.

• v.scanner: use precomputed character tables instead of checks
• v.scanner: use util.func_char_table in Scanner.ident_name/0
• v.scanner: restore the checks in ident_name, instead of using util.func_char_table
• v.scanner: split long condition in ident_name into several smaller ones
• v.scanner: use substr_unsafe in Scanner.ident_name/0 and Scanner.num_lit/2
• Revert "v.scanner: use substr_unsafe in Scanner.ident_name/0 and Scanner.num_lit/2"
• v.scanner: move non_whitespace_table to v.util
• v.scanner: use util.func_char_table[c] and util.name_char_table[c] directly
• v.util: cleanup the table generating functions, by using the builtin u8 methods

[spytheman]

With clang:

[spytheman]

With gcc, the speedup is very modest (under 1%), and sometimes (rarely), the old version is slightly faster (i.e. it is on the margin for error on my machine).

With tcc, the speedup is consistently around 1-2% for the scanner.

[felipensp]

Nice, good job!

[medvednikov]

Great job! Hyperfine reports ~4% though, not 1-2%?

[JalonSolov]

Probably dependent on the hardware where you run it. CPU speed, memory speed, etc. can all affect code running speed.