Add script to find linkerscript-defined info

Add ls_parse.py, a script to discover symbols whose values are defined
in a linker script, and valid memory extents corresponding to sections
in an object file. ls_parse can emit this information as a C file,
suitable for compiling into a goto-binary and linking with the rest of
the codebase. ls_parse can also emit the information as a JSON file,
suitable for automatic processing from within goto-cc. This supports
CPROVER in knowing the actual values of symbols that are not defined in
the C source.

CR: https://cr.amazon.com/r/7191907/

Author: karkhaz