feat: add focus hint outline border radius setting

Previously, the focus hint outline border radius was not exposed in the
preferences window becauses I wanted to cut down on the number of
settings. However, since the previous commit added already added another
setting to make the focus hint a border only, I might as well expose
this one too.

tiling-assistant@leleat-on-github/prefs.js

@@ -101,6 +101,7 @@ export default class Prefs extends ExtensionPreferences {
             'screen-right-gap',
             'screen-bottom-gap',
             'focus-hint-outline-size',
+            'focus-hint-outline-border-radius',
             'toggle-maximize-tophalf-timer',
             'vertical-preview-area',
             'horizontal-preview-area'

tiling-assistant@leleat-on-github/src/ui/prefs.ui

@@ -382,6 +382,19 @@
               </property>
             </object>
           </child>
+          <child>
+            <object class="AdwSpinRow" id="focus_hint_outline_border_radius">
+              <property name="title" translatable="yes" comments="Translators: This is a setting under the 'Focus Hint' preference group in the 'General' tab in the prefs window to set the size of the focus hint border radius">Outline Border Radius</property>
+              <property name="activatable-widget">focus_hint_outline_border_radius</property>
+              <property name="adjustment">
+                <object class="GtkAdjustment">
+                  <property name="upper">50</property>
+                  <property name="step-increment">1</property>
+                  <property name="page-increment">8</property>
+                </object>
+              </property>
+            </object>
+          </child>
         </object>
       </child>
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