Fix '<b>' did not get bold in HearingDevice footer.

Root Cause: Did not use <![CDATA[ ...]]> to represent it contains html tag <b>.

Solution: Use <![CDATA[ and Html.fromHtml to add Spanned for the footer string.

Bug: 378806589
Test: Enable bold text to test the effect
Flag: EXEMPT bugfix
Change-Id: I56827dc18e7183c0458c83dac0dbeca7eb8bb16d

src/com/android/settings/accessibility/HearingDeviceFooterPreferenceController.java

@@ -17,6 +17,7 @@
 package com.android.settings.accessibility;
 
 import android.content.Context;
+import android.text.Html;
 
 import androidx.annotation.NonNull;
 import androidx.preference.PreferenceScreen;
@@ -42,6 +43,13 @@ public class HearingDeviceFooterPreferenceController extends
 
         final AccessibilityFooterPreference footerPreference =
                 screen.findPreference(getPreferenceKey());
+        // We use html tag inside footer string, so it is better to load from html to have better
+        // html tag support.
+        final CharSequence title = Html.fromHtml(
+                mContext.getString(R.string.accessibility_hearing_device_footer_summary),
+                Html.FROM_HTML_MODE_COMPACT, /* imageGetter= */ null, /* tagHandler= */ null);
+        footerPreference.setTitle(title);
+
         // Need to update contentDescription string to announce "than" rather than ">"
         final String summaryTts = mContext.getString(
                 R.string.accessibility_hearing_device_footer_summary_tts);