Update py-meson to 0.47.2

Highlights:

      find_library: Use _build_wrapper to get library dirs
      python.find_installation: only try to find python with the
        py launcher if it isn't in PATH
      Fix @CURRENT_SOURCE_DIR@ in generator()
      Fix directory verification. Closes #3857.
      Add 32 bit sparc processor support. Closes #3901.
      Add support for s390x CPUs. Closes #3897.
      mesonbuild: Recognise risc-v architecture
      configure_file: Don't optimize away substitutions
      environment: Map mipsel -> mips, mips64el -> mips64
      Add new method: mlog.deprecation()
      Raise a MesonException when substituting an invalid value
      Print a more usable message when a subproject fails to configure
      get_library_naming: Use templates instead of suffix/prefix pairs
      find_library: Fix manual searching on OpenBSD
      find_library: Fix priority of library search in OpenBSD
      find_library: Validate and sort globbed shared library files
      gnome.gdbus_codegen: Handle XML docbook in subdirs
      Print a useful error when a compiler is not found in the cross file
      Add a feature-new entry for UserFeatureOption
      PkgConfigDependency: Fix library path search order
      Don't check version for fallback not-found dependency
      PkgConfigDependency: Parse library paths in a separate step
      find_library: Allow undefined symbols while linking
      Test that system shlibs with undefined symbols can be found
      Make the dependency order deterministic.
      Make the rpath order deterministic.


(prlw1)