Some CMake improvements

[LecrisUT]

• Bump the maximum CMake policy
• Use GNUInstallDirs as defaults to simplify donwstream's packaging

The first change could technically be problematic if an old policy is implicitly used, but these are generally unlikely. The motivation for that is to simplify downstream maintenance in the long run. CI builds should pick up any issues

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[pbhandar2]

Thank you for the PR! Could you explain the reason for bumping cmake version? It sets a minimum of 3.5 but newer versions can be used. I am not sure how the range would work with setting the minimum version of cmake with cmake_minimum_required.

[LecrisUT]

This sets a maximum (tested) cmake version policy. I.e. if you run with any CMake version less than the upper-bound, it will set all its policies to NEW. If you run with a CMake version greater than that, it will set all policies defined up to the upper-bound to NEW.

In practice it says upstream has tested up to this CMake version and all is fine. This reduces the downstream burden having to patch the lower-bound when CMake removes the support for that version (probably next batch is everything below 3.10)