Merges the fields that are set in desc_to_merge into the fields in this, without copying
allocated fields.
This is like [[email protected]], but only a shallow copy is made of the family name and other allocated fields.
this can only be used until desc_to_merge is modified or freed. This is meant to be used
when the merged font description is only needed temporarily.
| this |
a `PangoFontDescription` |
| desc_to_merge |
the `PangoFontDescription` to merge from |
| replace_existing |
if true, replace fields in this with the corresponding values
from |