textchildanchor: allow to specify replacement character
Currently text anchors with widgets will be represented as GTK_TEXT_UNKNOWN_CHAR
.
For some use cases (e.g. inlay hints in gnome-builder#1317) it would be nice if the replacement character could be specified by the app.
The following MR allows to create new text anchors with a different replacement character then the default GTK_TEXT_UNKNOWN_CHAR
by introducing gtk_text_child_anchor_new_with_replacement
.
Tests were added for the default and custom replacement character.
(Happy to back port it to gtk 3 if this gets merged)