Move all cmake package config template files into a single cmake/package/
directory:
- CppUTestConfig.cmake.install.in (from repo root)
- CppUTestConfig.cmake.build.in (from repo root)
- CppUTestConfig.cmake.autotools.in (from build/cmake_package_files/)
- CppUTestTargets.cmake.autotools.in (from build/cmake_package_files/)
- CppUTestTargets-relwithdebinfo.cmake.autotools.in (from build/cmake_package_files/)
- CppUTestConfigVersion.cmake (from build/cmake_package_files/)

Also remove the stale pre-generated static cmake files from
build/cmake_package_files/ that are superseded by the autotools templates.

Update cmake/install.cmake and Makefile.am with the new paths.

Consolidate all packaging-related template files into a top-level pkg/
directory, replacing the cmake/package/ directory introduced in the
previous commit:

- pkg/CppUTestConfig.cmake.install.in
- pkg/CppUTestConfig.cmake.build.in
- pkg/CppUTestConfig.cmake.autotools.in
- pkg/CppUTestTargets.cmake.autotools.in
- pkg/CppUTestTargets-relwithdebinfo.cmake.autotools.in
- pkg/CppUTestConfigVersion.cmake
- pkg/cpputest.pc.in

Using a generic pkg/ directory rather than cmake/package/ better reflects
that the directory covers multiple packaging systems (cmake and pkg-config).

Update cmake/install.cmake, configure.ac, and Makefile.am accordingly.

Switch from include(cmake/install.cmake) to add_subdirectory(pkg), which
is more idiomatic CMake and lets pkg/CMakeLists.txt use relative paths for
files in the same directory instead of ${PROJECT_SOURCE_DIR}/pkg/ prefixes.

Update PROJECT_SOURCE_DIR-relative paths for files outside pkg/ (the cmake/
Modules and Scripts directories, and the project include/ directory).

The autotools install was missing two cmake modules needed for downstream
consumers to use cpputest_discover_tests():

- CppUTest.cmake and _CppUTestDiscovery.cmake were not listed in
  cmakemodules_DATA in Makefile.am
- CppUTestConfig.cmake.autotools.in did not append the Modules directory
  to CMAKE_MODULE_PATH, so include(CppUTest) would fail even if the files
  were present

Both are present in the CMake install; bring the autotools install into
parity.

The autotools-installed cmake targets used bare names (CppUTest,
CppUTestExt) while the CMake install exports them with the CppUTest::
namespace (CppUTest::CppUTest, CppUTest::CppUTestExt). Downstream
consumers using target_link_libraries with the namespaced form would
silently get an error or unresolved target.

Update all three autotools cmake package templates to use the CppUTest::
namespace, matching what cmake's install(EXPORT ... NAMESPACE CppUTest::)
generates.

…tput

The templates were modelled on old cmake export file format. Rewrite them
to match the format cmake generates today:

- Use _cmake_ prefixed temporaries instead of _targetsDefined etc.
- Use 'IN LISTS "_cmake_import_check_files_for_${target}"' to safely
  reference variable names containing :: without cmake parsing issues
- Use _cmake_import_check_targets/_cmake_import_check_files_for_* instead
  of the old _IMPORT_CHECK_* names
- Update cmake_policy version range
- Add INTERFACE_LINK_LIBRARIES "CppUTest::CppUTest" to CppUTestExt so
  that linking against CppUTest::CppUTestExt pulls in CppUTest::CppUTest

Adds an "Autotools Custom prefix install" matrix entry that:
- Configures with a non-standard --libdir depth (lib/x86_64-linux-gnu)
  to exercise the install path computation in the cmake package files
- Installs directly (no DESTDIR) so cmake can consume the result
- Builds the examples against the installed package via find_package,
  confirming that headers, libraries, and cmake modules are all found
  correctly

Two new conditional steps are added to the autotools job:
- "Set install paths" computes INSTALL_PREFIX and INSTALL_LIBDIR from
  the matrix install_prefix value, keeping the path defined once
- "Consume with CMake" runs the examples build against the install

The separate CppUTestTargets-relwithdebinfo.cmake.autotools.in file was
mimicking cmake's multi-configuration pattern, which doesn't apply to
autotools. Autotools produces a single build output, so IMPORTED_LOCATION
(no config suffix) is the correct cmake idiom and works for all
downstream build types.

Move the library locations directly into CppUTestTargets.cmake.autotools.in
and delete the now-unnecessary config-specific template.

…cmake package

The cmake install sets INTERFACE_COMPILE_OPTIONS on CppUTest::CppUTest to
force-include MemoryLeakDetectorForceInclude.h, wiring up leak detection
automatically for downstream cmake consumers. The autotools cmake package
was missing this, requiring consumers to add the force-include manually.

Add the same property to the autotools targets template, conditioned on
whether memory leak detection was enabled at configure time (it is also
implicitly disabled by --disable-std-c). The memory_leak_detection
configure variable is AC_SUBST'd so its value is baked into the Makefile
and passed to sed as a literal string at install time.