[lld][WebAssemlby] Improve support for -L / -l and add testing

- Add support -Bdynamic/-Bstatic and their aliases
- Add support for `--library` and `--library-path` long form args
- Add test based on test/ELF/libsearch.s
- In `-Bdynamic` mode search for `.so` files in preference to `.a`.
- Unlike ELF continue to default to static mode until `-pie` or
  `-shared` are used.

Differential Revision: https://reviews.llvm.org/D135087