pango: upgrade 1.50.11 -> 1.50.12

Overview of changes in 1.50.12, 18-11-2022
==========================================
- Fix weight conversion on MacOS
- Update to Unicode 15
- Some introspection annotation fixes
- Improve PangoAttrList serialization
- Fix char offset calculatiosn in multi-paragraph
  layouts

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 35fc61a1)
Signed-off-by: Steve Sakoman <steve@sakoman.com>