Update Sphinx

• Repocopy textproc/py-sphinx to textproc/py-sphinx18
  
  Update it to 1.8.5 (latest version from 1.8.X). This version supports Python 2 and 3. Add test target.

• textproc/py-sphinx: Update to 3.0.2
  
  Python 3 only (3.5+). Add test target.

• Mk/Uses/python.mk: Add PY_SPHINX
  
  Shared macro to use with flavors and not break ports with USES=python (all versions).
  
  Python >=3.5 --> textproc/py-sphinx (v3.0.2) Python < 3.5 --> textproc/py-sphinx18 (v1.8.5)
  
  All ports that uses sphinx were changed to use the new variable ${PY_SPHINX} in the dependency line, exceptions:
  • Ports that fails to build with sphinx 3.0.2 because of code. They are pointing to textproc/py-sphinx18 directly. There aren't many ports.
  • Ports that doesn't know Python flavors.

• Add several patches to fix Sphinx consumers
  
  The most common issues are related with pkg-plist, the output files from Sphinx changes between versions, keep this dynamically is the better approach.
  
  This will save time in future sphinx updates.

PR: 245629
Exp-run by: antoine