Polish humanize strings for extra dim page

- Add intro for purpose or behavior
- Update footer description on usage, availability, or limitations

Bug: 218408553
Test: Manual testing
Change-Id: I3951959263e30e7525a44950c38374366eaf69c7

res/values/strings.xml

@@ -5617,10 +5617,11 @@
     <string name="reduce_bright_colors_preference_summary" product="default">Dim screen beyond your phone\u2019s minimum brightness</string>
     <!-- Summary for the accessibility preference to configure Reduce Brightness feature. [CHAR LIMIT=NONE] -->
     <string name="reduce_bright_colors_preference_summary" product="tablet">Dim screen beyond your tablet\u2019s minimum brightness</string>
+    <!-- Intro that describes Reduce Brightness. [CHAR LIMIT=NONE] -->
+    <string name="reduce_bright_colors_preference_intro_text">Make your screen dimmer so it\u2019s more comfortable to read</string>
     <!-- Subtitle that describes Reduce Brightness. [CHAR LIMIT=NONE] -->
     <string name="reduce_bright_colors_preference_subtitle" product="default">
-        <![CDATA[Make your screen dimmer so it\u2019s more comfortable to read.<br/><br/>
-        This can be helpful when:
+        <![CDATA[Extra dim can be helpful when:
         <ol>
             <li>\u00a0Your phone\u2019s default minimum brightness is still too bright</li>
             <li>\u00a0You\u2019re using your phone in dark situations, like at night or in a dark room before bed</li>
@@ -5629,8 +5630,7 @@
     </string>
     <!-- Subtitle that describes Reduce Brightness. [CHAR LIMIT=NONE] -->
     <string name="reduce_bright_colors_preference_subtitle" product="tablet">
-        <![CDATA[Make your screen darker so it\u2019s more comfortable to read.<br/><br/>
-        This can be helpful when:
+        <![CDATA[Extra dim can be helpful when:
         <ol>
             <li>\u00a0Your tablet\u2019s default minimum brightness is still too bright</li>
             <li>\u00a0You\u2019re using your tablet in dark situations, like at night or in a dark room before bed</li>

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

@@ -68,6 +68,7 @@ public class ToggleReduceBrightColorsPreferenceFragment extends ToggleFeaturePre
         mComponentName = REDUCE_BRIGHT_COLORS_COMPONENT_NAME;
         mPackageName = getText(R.string.reduce_bright_colors_preference_title);
         mHtmlDescription = getText(R.string.reduce_bright_colors_preference_subtitle);
+        mTopIntroTitle = getText(R.string.reduce_bright_colors_preference_intro_text);
         mRbcIntensityPreferenceController =
                 new ReduceBrightColorsIntensityPreferenceController(getContext(), KEY_INTENSITY);
         mRbcPersistencePreferenceController =