Improvement: Update gtest

[Davknapp]

Closes #2097

Removes the thirdparty folder and uses the FetchContent-Feature of Cmake.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.35%. Comparing base (e437ebe) to head (d422773).
⚠️ Report is 44 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2105   +/-   ##
=======================================
  Coverage   77.34%   77.35%           
=======================================
  Files         113      113           
  Lines       19099    19124   +25     
=======================================
+ Hits        14772    14793   +21     
- Misses       4327     4331    +4     

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[sandro-elsweijer]

Suggested change

$<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}>

[Davknapp]

we still need it while configuring the fortran interace.