Cleanup use of CMake version in install destinations
Factor the CMAKE_DATA_DIR, CMAKE_DOC_DIR, and CMAKE_MAN_DIR selection out of CMakeLists.txt and into a Source/CMakeInstallDestinations.cmake script. Load the script from the original location of the code. Cache the destination values as empty strings so we know if the user sets them explicitly. If not, then compute defaults based on the platform and full CMake version string. By not caching the versioned defaults, we can change them in a single build tree as the version changes. Remove duplication of the install destination defaults from the bootstrap script. Cache empty defaults there too. Parse from the CMake code the default values to report in the help output. Keep the CMake code in a structured format to make this reliable.
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