refactor(rez-pip): use dist info metadata attributes
refactor(rez-pip): use dist info metadata attributes

Use metadata attributes to retrieve core data such as the
name, version and summary of the requested package.

Relates https://www.python.org/dev/peps/pep-0426/#core-metadata, https://github.com/nerdvegas/rez/issues/475, https://github.com/nerdvegas/rez/issues/503

instinct-vfx/rez,nerdvegas/rez,nerdvegas/rez,instinct-vfx/rez