Fixed source-generated class names

[CronKz]

• Replace all special characters with an underscore
• Ensure the first letter is either an underscore or letter

Closes #7801

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7819   +/-   ##
=======================================
  Coverage        ?   74.31%           
=======================================
  Files           ?     2871           
  Lines           ?   149806           
  Branches        ?    17417           
=======================================
  Hits            ?   111333           
  Misses          ?    32672           
  Partials        ?     5801           

Flag	Coverage Δ
unittests	74.31% <ø> (?)

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