Update cmake.in to reference exported dependencies

[lemirep]

Those are PRIVATE libraries we link against but when consuming the KDUtils or KDGui package from vcpkg we need to have provided a way to find those targets.

[lemirep]

Essentially without this patch I'm getting:

[cmake] CMake Error at build/Debug/vcpkg_installed/x64-linux/share/KDUtils/KDUtilsConfigTargets.cmake:60 (set_target_properties):
[cmake] The link interface of target "KDUtils::KDUtils" contains:
[cmake]
[cmake] mio::mio
[cmake]
[cmake] but the target was not found. Possible reasons include:
[cmake]
[cmake] * There is a typo in the target name.
[cmake] * A find_package call is missing for an IMPORTED target.
[cmake] * An ALIAS target is missing.
[cmake]
[cmake] Call Stack (most recent call first):
[cmake] build/Debug/vcpkg_installed/x64-linux/share/KDUtils/KDUtilsConfig.cmake:14 (include)
[cmake] vcpkg/scripts/buildsystems/vcpkg.cmake:904 (_find_package)
[cmake] cmake/dependencies.cmake:12 (find_package)
[cmake] CMakeLists.txt:145 (include)
[cmake]
[cmake]
[cmake] CMake Error at build/Debug/vcpkg_installed/x64-linux/share/KDGui/KDGuiConfigTargets.cmake:60 (set_target_properties):
[cmake] The link interface of target "KDUtils::KDGui" contains:
[cmake]
[cmake] Wayland::Client
[cmake]
[cmake] but the target was not found. Possible reasons include:
[cmake]
[cmake] * There is a typo in the target name.
[cmake] * A find_package call is missing for an IMPORTED target.
[cmake] * An ALIAS target is missing.
[cmake]
[cmake] Call Stack (most recent call first):
[cmake] build/Debug/vcpkg_installed/x64-linux/share/KDGui/KDGuiConfig.cmake:14 (include)
[cmake] vcpkg/scripts/buildsystems/vcpkg.cmake:904 (_find_package)
[cmake] cmake/dependencies.cmake:14 (find_package)
[cmake] CMakeLists.txt:145 (include)
[cmake]

The fundamental issue is that PRIVATE in CMake means "don't propagate to consumers during build", but it doesn't mean "won't be needed by consumers at link time". Even if those PRIVATE dependencies are static libraries, they could become link-time dependencies because:

• The static library contains object files with unresolved symbols
• Those symbols must be resolved when creating the final executable
• CMake conservatively includes them in the export information