Fix for Introductory tech level also showing Standard equipment in non-VTL mode.

[Sleet01]

While exploring our Equipment filtering code as part of #1696 , I found that we are incorrectly applying the "Introductory" tech level filter in such a way that it always shows up to Standard-level equipment instead.

The fix is to use an existing function in SimpleTechLevel to get the correct enum value from the Tech Level combobox, which prevents the exception that defaults to Standard tech level.

Testing:

• Ran all 3 projects' unit tests
• Confirmed Tech Level selection now works correctly in the UI
• Confirmed non-VTL tech advancement follows the process outlined in [Issue] Availability Year doesn't seem to be enforced properly #1696 comments

Close #1696

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.13%. Comparing base (b844630) to head (a493832).
Report is 8 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##             master   #1698   +/-   ##
========================================
  Coverage      2.13%   2.13%           
  Complexity      209     209           
========================================
  Files           271     271           
  Lines         31380   31380           
  Branches       5341    5341           
========================================
  Hits            670     670           
  Misses        30553   30553           
  Partials        157     157           

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