Add test for CMake config files installed by B2

[Flamefire]

I factored out the test script to consume the library with CMake.
This is then used in 2 steps:

• On the library installed with CMake (as before)
• new: Same but installed with B2

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (734e1fd) to head (2075d39).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #332   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines           24        24           
  Branches        11        11           
=========================================
  Hits            24        24           

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