Use pyelftools to extract the symbol table from the
link stage executable. Then, filter out the function names
and sort them based on their offsets before writing into the
`symtab.c`, this is similar to how the `isr_tables` works.
To access the structure, simply include the new header:
```c
#include <zephyr/debug/symtab.h>
```
Signed-off-by: Yong Cong Sin <ycsin@meta.com>
