Add Intersphinx mapping for use across PSE+ projects

[dangunter]

Fixes

Issue #1468

Changes proposed in this PR:

• Create a tiny python module that can be used by other dependent projects to retrieve a canonical intersphinx mapping inside another projects' conf.py:

from idaes.util.intersphinx import get_intersphinx_mapping
# ...
intersphinx_mapping = get_intersphinx_mapping()
intersphinx_mapping.update({}) # add local mappings here

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1. I agree my contributions are submitted under the license terms described in the LICENSE.txt file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.36%. Comparing base (94a3043) to head (95c79cf).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1469   +/-   ##
=======================================
  Coverage   76.36%   76.36%           
=======================================
  Files         394      395    +1     
  Lines       64953    64977   +24     
  Branches    14404    14408    +4     
=======================================
+ Hits        49601    49622   +21     
- Misses      12793    12797    +4     
+ Partials     2559     2558    -1     

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[dangunter]

Once this is merged it will be used in the idaes/examples, see IDAES/examples#132

[dangunter]

Too complex