cmake: keep private include dirs out of dependencies

[tomatotomata]

Summary

• keep CMake target-private include directories on the converted target only
• expose only INTERFACE include directories through the generated Meson dependency
• preserve public and private include paths for the target itself

Fixes #13818

Validation

• python -m compileall -q mesonbuild/cmake
• git diff --check
• python -m pytest -q unittests --disable-warnings --maxfail=1 (blocked by the environment: pytest-recording and pytest-vcr are both installed)
• run_tests.py was blocked because Ninja is not installed in this environment