FindGTK2: Add harfbuzz target for dependency from pango
Since !3877 (merged), pango's dependency on harfbuzz has been captured, but only for the GTK2_INCLUDE_DIRS
and GTK2_LIBRARIES
variables. Add the GTK2::harfbuzz
imported target and update the GTK2::pango
target to depend on it.
Issue: #19531 (closed)
Backport: release