feat: find references to enumerators

[stigh]

When using the "Find All References" in vscode for an enumerator, it previously found no matches.

[codecov]

Codecov Report

❌ Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.37%. Comparing base (3bc2031) to head (0aa234b).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
fortls/parsers/internal/utilities.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #515      +/-   ##
==========================================
- Coverage   44.39%   44.37%   -0.02%     
==========================================
  Files          35       35              
  Lines        4800     4804       +4     
==========================================
+ Hits         2131     2132       +1     
- Misses       2669     2672       +3     

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[stigh]

#533 can be merged before this one to fix the test failures.