use default button action instead of adding a new one (relation reference and editor widgets)
use layer's displayExpression in relation reference widget line edit
[editwidgets] text color for r/o line edits matches disabled color

Line edits are set to readonly to make it possible to copy values from disabled
forms. Unfortunately Qt uses a style that makes them look editable even though
they are not. This patches the text color to have the appearance that hints an
uneditable widget.

Fix #11413
fix deprecation warnings
fix where clase when multiple features are filtered by id (fixes #11336, fixes #11408)
allow setting visiblity of selected layers (fixes #10835)
avoid creating a histogram without range (fixes #10832)
fix geography detection (fixes #11375)
Incomplete line image symbol renderer