[BUILD] Visual Studio GMOCK_LIB issues and explicit c++17

[bkuschel]

• Change in PR [TEST] Fix linking order and gmock linking #3106 broke MSVC build. GMOCK_LIB-NOTFOUND from cmake.
• In some cases (unsure why), c++17 has to be set explicitly for MSVC

Changes

• Copy over similar working code into cmake files dealing with GMOCK_LIB
• Explicitly add c++17 support for MSVC

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

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[marcalff]

Thanks for the patch.

This needs more investigations, to understand the root cause.

[marcalff]

We can not have that, this will break everybody.

[bkuschel]

I'll try to find an alternative

[bkuschel]

@marcalff The only other way I can get it to compile with vs2022 is to add "-DWITH_STL=CXX14"
Other wise i get

warning STL4038: The contents of <string_view> are available only with C++17 or later.
C:\Users\Administrator\Git\opentelemetry-cpp\api\include\opentelemetry/std/string_view.h(18): error C2039: 'string_view': is not a member of 'std'

This is during stl build, nostd works without this (of course).

[owent]

You can use -DCMAKE_CXX_STANDARD=17 when running cmake command to use C++17 in your environment.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.86%. Comparing base (fe68d51) to head (c280540).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3158   +/-   ##
=======================================
  Coverage   87.86%   87.86%           
=======================================
  Files         195      195           
  Lines        6151     6151           
=======================================
  Hits         5404     5404           
  Misses        747      747           

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