pangomm: updated to 2.46.3

2.46.3 (stable):

* Context::get_font_map(): Fix reference count

Build:
* Meson build: Specify 'check' option in run_command()
  Will be necessary with future versions of Meson.
* Meson build: Check if Perl is required for building documentation
* Meson build: Avoid unnecessary configuration warnings
* Meson build: Re-organize warning-related compiler flags for MSVC

(adam)