Move String's 46 method definitions from runtime
mrb_define_method_id() calls to a static ROM method table
sorted at init time. mrb_mt_init_rom() sorts the parallel
vals/keys arrays by presym ID and sets the readonly flag.
Expose mt_tbl and related types in internal.h so ROM tables
can be defined in individual source files.
When MRB_NO_PRESYM is defined, falls back to traditional
runtime method registration.
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto
96da40605f