[MaterialDatePicker][a11y] Make picker header focusable to improve TalkBack response

PiperOrigin-RevId: 440375456

Author: paulfthomas

lib/java/com/google/android/material/datepicker/res/layout-land/mtrl_picker_header_dialog.xml

@@ -37,7 +37,9 @@
       android:layout_height="0dp"
       android:layout_weight="1"
       android:paddingStart="@dimen/mtrl_calendar_header_text_padding"
-      android:paddingLeft="@dimen/mtrl_calendar_header_text_padding">
+      android:paddingLeft="@dimen/mtrl_calendar_header_text_padding"
+      android:focusable="true"
+      android:focusableInTouchMode="true">
 
       <include layout="@layout/mtrl_picker_header_title_text"/>
       <include layout="@layout/mtrl_picker_header_selection_text"/>

lib/java/com/google/android/material/datepicker/res/layout/mtrl_picker_header_dialog.xml

@@ -38,7 +38,9 @@
       android:layout_height="match_parent"
       android:layout_weight="1"
       android:paddingStart="@dimen/mtrl_calendar_header_text_padding"
-      android:paddingLeft="@dimen/mtrl_calendar_header_text_padding">
+      android:paddingLeft="@dimen/mtrl_calendar_header_text_padding"
+      android:focusable="true"
+      android:focusableInTouchMode="true">
 
       <include layout="@layout/mtrl_picker_header_title_text"/>
       <include layout="@layout/mtrl_picker_header_selection_text"/>

lib/java/com/google/android/material/datepicker/res/layout/mtrl_picker_header_fullscreen.xml

@@ -53,7 +53,9 @@
       android:layout_height="match_parent"
       android:layout_weight="1"
       android:paddingStart="@dimen/mtrl_calendar_header_text_padding"
-      android:paddingLeft="@dimen/mtrl_calendar_header_text_padding">
+      android:paddingLeft="@dimen/mtrl_calendar_header_text_padding"
+      android:focusable="true"
+      android:focusableInTouchMode="true">
 
       <TextView
         android:id="@+id/mtrl_picker_title_text"