Add test cases for Layout.primaryIsTrailingPrevious

Bug: 78464361
Test: atest FrameworksCoreTests:android.text.LayoutTest
Change-Id: Id2735e993849bced47f9b361c99e13f91fe88070
diff --git a/core/java/android/text/Layout.java b/core/java/android/text/Layout.java
index aa97b2a..9dd3ce2 100644
--- a/core/java/android/text/Layout.java
+++ b/core/java/android/text/Layout.java
@@ -1004,7 +1004,9 @@
         return TextUtils.packRangeInLong(0, getLineEnd(line));
     }
 
-    private boolean primaryIsTrailingPrevious(int offset) {
+    /** @hide */
+    @VisibleForTesting
+    public boolean primaryIsTrailingPrevious(int offset) {
         int line = getLineForOffset(offset);
         int lineStart = getLineStart(line);
         int lineEnd = getLineEnd(line);