It uses BER number compression of delta of instruction positions and line
numbers. BER compression is a variable length number representation.
* `mrb_debug_line_ary`: array of line numbers represented in `uint16_t`.
`[lineno, lineno, ...]`
* `mrb_debug_line_flat_map`: array of `mrb_irep_debug_info_line`, which
is `struct {uint32_t pos; uint16_t lineno}`, for each line.
* `mrb_debug_line_packed_map` [new]: sequence of BER compressed 2
numbers, `pos_delta, lineno_delta`. Deltas are differences from
previous values (starting `0`). `line_entry_counts` represents total
length of a packed map string for this type.
The addresses for packed inline symbols reference `mrb->symbuf` that
could be overridden by the later call of `mrb_sym2name_len`. Since
file names in call stack information are kept as symbols, keeping the
address in the C structures could cause problems like #4342.
This changes small incompatible changes in function prototypes:
* `mrb_parser_get_filename`: return value changed to `mrb_sym`.
* `mrb_debug_get_filename`: add `mrb_state*` as a first argument.
* `mrb_debug_get_line`: ditto.
I believe above functions are almost internal, and no third-party
mrbgem use them.
John Bampton