Make sure we use a canonical name for all packages and references to packages in requirements

[JeanChristopheMorinPerso]

Fixes #55.

• Add tests.
• Document this package name conversion properly.
• Add a big warning in the release notes since this is a breaking change.

[codecov]

Codecov Report

Merging #57 (d14f3d3) into main (9c61a5d) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #57   +/-   ##
=======================================
  Coverage   77.57%   77.57%           
=======================================
  Files           8        8           
  Lines         709      709           
  Branches      147      147           
=======================================
  Hits          550      550           
  Misses        151      151           
  Partials        8        8           

Files	Coverage Δ
src/rez_pip/utils.py	76.03% <100.00%> (ø)