CMake 3.27 deprecates compatibility with CMake < 3.5.  Update tests that
do not cover older interfaces to avoid the deprecation warning.

Follow the pattern from:

* commit 7b07ccdd2b (Tests/*Only: Update cmake_minimum_required versions,
                     2020-06-15, v3.19.0-rc1~629^2~1)

* commit 72e7c45e98 (Tests: Bump CMake minimum required in tests to 2.8.12,
                     2020-12-22, v3.20.0-rc1~224^2)

* commit f6b4db365a (Tests: bump cmake_minimum_required version to 2.8.12,
                     2021-04-04, v3.21.0-rc1~372^2)

Also remove explicit `cmake_policy` settings made redundant by the
version.

This CPack generator has been deprecated since commit 7bf187499f
(CPack: Deprecate PackageMaker generator, 2020-01-31).

Fixes: #23344

This needlessly produces warnings during the test runs that no-one
sees but that are distracting when actually inspecting the logs.

GitLab now uses a `/-/` component between the `group/project` part of
the URL and the `{issues,merge_requests,tree}` part so that it can
support `group/subgroup/project` with arbitrary depth.

Run the `clang-format.bash` script to update our C and C++ code to a new
include order `.clang-format`.  Use `clang-format` version 6.0.

Without `CPACK_VERBATIM_VARIABLES` a path with backslashes does not make
it through `CPackConfig.cmake` properly.  Just use forward slashes which
NSIS seems to understand anyway.

References to specific comments are left as-is since comments were not
migrated.

The latter is now the preferred URL for visiting cmake.org with a
browser.  Convert using the shell code:

 git ls-files -z | xargs -0 sed -i 's|http://www\.cmake|https://cmake|g'

Ancient versions of CMake required else(), endif(), and similar block
termination commands to have arguments matching the command starting the
block.  This is no longer the preferred style.

Run the following shell code:

for c in else endif endforeach endfunction endmacro endwhile; do
    echo 's/\b'"$c"'\(\s*\)(.\+)/'"$c"'\1()/'
done >convert.sed &&
git ls-files -z -- bootstrap '*.cmake' '*.cmake.in' '*CMakeLists.txt' |
egrep -z -v '^(Utilities/cm|Source/kwsys/)' |
egrep -z -v 'Tests/CMakeTests/While-Endwhile-' |
xargs -0 sed -i -f convert.sed &&
rm convert.sed

Our Git commit hooks disallow modification or addition of lines with
trailing whitespace.  Wipe out all remnants of trailing whitespace
everywhere except third-party code.

Run the following shell code:

git ls-files -z -- \
 bootstrap doxygen.config '*.readme' \
 '*.c' '*.cmake' '*.cpp' '*.cxx' \
 '*.el' '*.f' '*.f90' '*.h' '*.in' '*.in.l' '*.java' \
 '*.mm' '*.pike' '*.py' '*.txt' '*.vim' |
egrep -z -v '^(Utilities/cm|Source/(kwsys|CursesDialog/form)/)' |
egrep -z -v '^(Modules/CPack\..*\.in)' |
xargs -0 sed -i 's/ \+$//'