Privacy Guide: Comprehensible a11y labels for completion step buttons

(cherry picked from commit a19720b)

Bug: 1446168
Change-Id: Ibd79ebb0b7f76116e428588306ace5238ea01b70
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4571021
Reviewed-by: Rainhard Findling <rainhard@chromium.org>
Commit-Queue: Rubin Deliallisi <rubindl@chromium.org>
Auto-Submit: Rubin Deliallisi <rubindl@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1150467}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4570898
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/5790@{#193}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

chrome/browser/privacy_guide/android/java/res/layout/privacy_guide_done.xml

@@ -47,6 +47,7 @@ found in the LICENSE file.
             android:layout_height="wrap_content"
             android:layout_marginBottom="@dimen/done_step_header_marginBottom"
             android:text="@string/privacy_guide_privacy_sandbox_heading"
+            android:labelFor="@+id/ps_button"
             style="@style/TextAppearance.TextMediumThick.Accent1" />
 
         <LinearLayout
@@ -83,6 +84,7 @@ found in the LICENSE file.
             android:layout_height="wrap_content"
             android:layout_marginBottom="@dimen/done_step_header_marginBottom"
             android:text="@string/privacy_guide_web_app_activity_heading"
+            android:labelFor="@+id/waa_button"
             style="@style/TextAppearance.TextMediumThick.Accent1" />
 
         <LinearLayout