Recommended update for gtk3

This update for gtk3 fixes the following issues:

- Add support for AtkTableCell. (bsc#1119306, fate#326548)
- Export gtk_cell_accessible_parent_get_(row|column)_header_cells_ functions.
(bsc#1121456)

This update was imported from the SUSE:SLE-15:Update update project.

Fixed bugs
bnc#1119306
a11y: AtkObjects should programmatically expose table cell information
bnc#1121456
libgtk-3.so does not export gtk_cell_accessible_parent_get_row_header_cells function but Gtk-3.0.gir has it listed
Selected Binaries
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