fix(cmake): improved cross-compilation support (#5083)

* fix(cmake): do not use Python::Interpreter when cross-compiling

* chore: apply cmake-format to pybind11NewTools.cmake

* fix(cmake): do not look for Python Interpreter component when cross-compiling

* feat(cmake): guess Python extension suffix

* fix: add pybind11GuessPythonExtSuffix.cmake to packaging test

* Use PYBIND11_CROSSCOMPILING instead of CMAKE_CROSSCOMPILING

* refactor: require PYBIND11_USE_CROSSCOMPILING

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

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Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>