Fix #1918050 [[Enhancement] Add clear buttons inside the text fields of the Smart device control screen](https://bugs.launchpad.net/calibre/+bug/1918050)

src/calibre/gui2/dialogs/smartdevice.ui

@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>612</width>
+    <width>618</width>
     <height>226</height>
    </rect>
   </property>
@@ -31,7 +31,7 @@
      </property>
      <property name="text">
       <string>&lt;p&gt;Start wireless device connections. Currently used only
-       by &lt;a href="https://calibrecompanion.co?utm_source=Calibre&amp;utm_medium=Software&amp;utm_campaign=Main&amp;utm_term=WirelessDeviceDialog"&gt;Calibre Companion&lt;/a&gt;.
+       by &lt;a href=&quot;https://calibrecompanion.co?utm_source=Calibre&amp;utm_medium=Software&amp;utm_campaign=Main&amp;utm_term=WirelessDeviceDialog&quot;&gt;Calibre Companion&lt;/a&gt;.
        &lt;p&gt;You may see some messages from your computer's firewall or anti-virus manager asking you if it is OK for calibre to connect to the network. &lt;b&gt;Please answer yes&lt;/b&gt;. If you do not, wireless connections will not work.</string>
      </property>
      <property name="wordWrap">
@@ -40,7 +40,6 @@
      <property name="openExternalLinks">
       <bool>true</bool>
      </property>
-
     </widget>
    </item>
    <item row="1" column="0">
@@ -84,6 +83,9 @@
      <property name="placeholderText">
       <string>Optional password for security</string>
      </property>
+     <property name="clearButtonEnabled">
+      <bool>true</bool>
+     </property>
     </widget>
    </item>
    <item row="2" column="2">
@@ -114,6 +116,9 @@
      <property name="placeholderText">
       <string>Optional port number</string>
      </property>
+     <property name="clearButtonEnabled">
+      <bool>true</bool>
+     </property>
     </widget>
    </item>
    <item row="4" column="2">