adding make_aps_key() function

[andy-beer]

Adds a public function for generating a key suitable for an AttributePropertySet property.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.27%. Comparing base (cd1d039) to head (df3e570).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #800 +/- ## ======================================= Coverage 83.27% 83.27% ======================================= Files 192 192 Lines 32913 32914 +1 ======================================= + Hits 27408 27409 +1 Misses 5505 5505 ```

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