pypy: translate and bottle

This translates and builds pypy with --shared. This changes the current behavior of the formula, which is to install the binary pypy from upstream. The improvement this represents over installing a binary pypy are better uWSGI support (#32642) and linkage against a current (brewed) OpenSSL. This can be bottled, so the "brew install pypy" user experience will be similar.

--shared replaces the pypy executable with a stub and moves the functional bits into a shared library, libpypy-c.dylib. 

The pypy binary tarball is downloaded and invoked to perform the translation, since translation takes at least 45 minutes with pypy, and is considerably faster with pypy than with CPython.

If there is a reason to prefer a brewed sqlite over system sqlite, that's controlled by setting DYLD_LIBRARY_PATH to include the sqlite keg at runtime. We could env_script or possibly caveat that if there's a good reason to do it.

If we like this approach, we can do the same for pypy3.