tdf#119931 tdf#130857 chart a11y: Set mnemonic widget in "Smooth Lines" dlg

Set the mnemonic widget, which e.g. makes the Orca screen
reader announce what the combo box is about ("Line Type")
when it receives focus with the gtk3 or qt6 vcl plugins on Linux.

For qt6 and the use of native Qt widgets
(SAL_VCL_QT_USE_WELDED_WIDGETS=1) this also fixes
that the labels text was previously shown as a literal
"Line &Type".

Change-Id: I2e699a10bdec27663b38a92d4091e647a6b7c49e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/208497
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Tested-by: Jenkins

chart2/uiconfig/ui/smoothlinesdlg.ui

@@ -110,6 +110,7 @@
                     <property name="can-focus">False</property>
                     <property name="label" translatable="yes" context="smoothlinesdlg|TypeLabel">Line _Type:</property>
                     <property name="use-underline">True</property>
+                    <property name="mnemonic-widget">SplineTypeComboBox</property>
                     <property name="xalign">0</property>
                   </object>
                   <packing>

solenv/sanitizers/ui/modules/schart.suppr

@@ -15,7 +15,6 @@ chart2/uiconfig/ui/sidebarerrorbar.ui://GtkSpinButton[@id='spinbutton_pos'] no-l
 chart2/uiconfig/ui/sidebarerrorbar.ui://GtkSpinButton[@id='spinbutton_neg'] no-labelled-by
 chart2/uiconfig/ui/sidebarerrorbar.ui://GtkLabel[@id='label5'] orphan-label
 chart2/uiconfig/ui/sidebarseries.ui://GtkLabel[@id='label_series_tmpl'] orphan-label
-chart2/uiconfig/ui/smoothlinesdlg.ui://GtkLabel[@id='TypeLabel'] orphan-label
 chart2/uiconfig/ui/titlerotationtabpage.ui://GtkLabel[@id='degreeL'] orphan-label
 chart2/uiconfig/ui/titlerotationtabpage.ui://GtkLabel[@id='labelABCD'] orphan-label
 chart2/uiconfig/ui/titlerotationtabpage.ui://GtkLabel[@id='textdirL'] orphan-label