Create a lookup table for magic vtables from magic type, PL_magic_data.

Create a lookup table for magic vtables from magic type, PL_magic_data.

Use it to eliminate the large switch statement in Perl_sv_magic().

As the table needs to be keyed on magic type, which is expressed as C character
constants, the order depends on the compiler's character set. Frustratingly,
EBCDIC variants don't agree on the code points for '~' and ']', which we use
here. Instead of having (at least) 4 tables, get the local runtime to sort the
table for us. Hence the regen script writes out the (unsorted) mg_raw.h, which
generate_uudmap sorts to generate mg_data.h