CMake updates

[galabovaa]

Apologies for a rather large PR. Build system updates and a rename of the source directory.

Added several tests for linking with CMake in https://github.com/ERGO-Code/highs-tests

• CMake targets in build dir now works: closes CMake Error when trying to linstall HiGHS as LP solver in SCIP (highs::highs not found) #2283
• More relocatable package using BUILD_INTERFACE.. in CMake Include cmake bux fix #2253
• long awaited rename of source dir from src/ to highs/ for better style and cleaner integration
• src/test is now highs/test_kkt to avoid the test/ in gitignore for CMake FetchContent

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.09%. Comparing base (0870d47) to head (9b8de43).
Report is 30 commits behind head on latest.

Additional details and impacted files

@@           Coverage Diff           @@
##           latest    #2286   +/-   ##
=======================================
  Coverage   79.08%   79.09%           
=======================================
  Files         343      343           
  Lines       83366    83376   +10     
=======================================
+ Hits        65933    65945   +12     
+ Misses      17433    17431    -2     

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[jajhall]

Only 452 files changed, but nothing that affects any of the source code files, so fine by me.