Roadmap to CMake 4.0

This is a tracking issue for specific changes the CMake maintainers plan for version 4.0.

In CMake 4.x versions:

• Renumber post-3.31 development from 3.32 to 4.0: !10183 (merged)

we can remove some compatibility with CMake 3.x versions and older:

• Simplify representation of removed policies: !9993 (merged)
• Remove compatibility with CMake versions older than 2.8.0: !10188 (merged)
• Remove compatibility with CMake versions older than 2.8.12: !10195 (merged)
• Remove compatibility with CMake versions older than 3.0: !10198 (merged)
• Remove compatibility with CMake versions older than 3.1: !10205 (merged)
• Remove Visual Studio generator pre-3.1 arch-specific names: #26481 (closed)
• Remove compatibility with CMake versions older than 3.2: !10210 (merged)
• Remove compatibility with CMake versions older than 3.3: !10210 (merged)
• Remove compatibility with CMake versions older than 3.4: !10210 (merged)
• Remove compatibility with CMake versions older than 3.5: !10210 (merged)
• Option to configure projects written for outdated CMake versions: #26698 (closed)

With a major version bump we can make long-desired changes that may require usage updates by clients, e.g., to remove work arounds, as these could not be made with a policy:

• Preserve symlinks in references to cmake itself: #19849 (closed), #21059 (closed)
• Remove path translation map: #16228 (closed)
• Windows: Avoid actual-case-on-disk lookup in low-level operations: #20214 (closed)
• Windows: Implement realpath (without resolving subst drives): #17206 (closed), #26750 (closed)
• macOS: Use system compilers without explicit SDK by default: #19180 (closed)
• Document policy removal schedule for the future: !10222 (merged)
• Modernize LICENSE file conventions: !10416 (merged)
• Cull list of supported systems to drop those that no longer work: #26496 EDIT: This can be deferred.

We can also make some code style updates:

• Update clang-format to version 18 and enforce "east const": #26123 (closed), !10225 (merged)