Revert "Temporarily revert "build: use `find_package(Python3)` if available""

This reverts commit 35edd704e0fda09e8e634515c0b451d4a8b6b914.

Revert the revert and extend the patch further to account for the use of
the `PYTHONINTERP_FOUND`.

GitOrigin-RevId: 216833b32befd14079130a3b857906f4e301179c
6 files changed