[symbolizer] Support symbol lookup

Recent versions of GNU binutils starting from 2.39 support symbol+offset
lookup in addition to the usual numeric address lookup. This change adds
symbol lookup to llvm-symbolize and llvm-addr2line.

Now llvm-symbolize behaves closer to GNU addr2line, - if the value specified
as address in command line or input stream is not a number, it is treated as
a symbol name. For example:

    llvm-symbolize --obj=abc.so func_22
    llvm-symbolize --obj=abc.so "CODE func_22"

This lookup is now supported only for functions. Specification with
offset is not supported yet.

Differential Revision: https://reviews.llvm.org/D149759