Replace existing Robolectric test task with functioning one.

This CL does the following:
- Creates a dir for multivalentTests
- Creates symlinks for the dir to keep Android Studio happy
- Moves many files to the multivalentTests dir
- Adjusts gradle and soong build files to use the new dir as part of
their source sets.

Test: ./gradlew :NexusLauncher:testGoogleWithQuickstepDebugUnitTest
Test: atest Launcher3RoboTests
Fix: 316553886
Bug: 316553889
Flag: NA
Change-Id: Iae28fd0c0191b3ecf9bd2950800875950cca2622

tests/multivalentTests/src/com/android/launcher3/util/GridOccupancyTest.java

@@ -0,0 +1,70 @@
+package com.android.launcher3.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import androidx.test.filters.SmallTest;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/**
+ * Unit tests for {@link GridOccupancy}
+ */
+@SmallTest
+@RunWith(AndroidJUnit4.class)
+public class GridOccupancyTest {
+
+    @Test
+    public void testFindVacantCell() {
+        GridOccupancy grid = initGrid(4,
+                1, 1, 1, 0, 0,
+                0, 0, 1, 1, 0,
+                0, 0, 0, 0, 0,
+                1, 1, 0, 0, 0
+        );
+
+        int[] vacant = new int[2];
+        assertTrue(grid.findVacantCell(vacant, 2, 2));
+        assertEquals(vacant[0], 0);
+        assertEquals(vacant[1], 1);
+
+        assertTrue(grid.findVacantCell(vacant, 3, 2));
+        assertEquals(vacant[0], 2);
+        assertEquals(vacant[1], 2);
+
+        assertFalse(grid.findVacantCell(vacant, 3, 3));
+    }
+
+    @Test
+    public void testIsRegionVacant() {
+        GridOccupancy grid = initGrid(4,
+                1, 1, 1, 0, 0,
+                0, 0, 1, 1, 0,
+                0, 0, 0, 0, 0,
+                1, 1, 0, 0, 0
+        );
+
+        assertTrue(grid.isRegionVacant(4, 0, 1, 4));
+        assertTrue(grid.isRegionVacant(0, 1, 2, 2));
+        assertTrue(grid.isRegionVacant(2, 2, 3, 2));
+
+        assertFalse(grid.isRegionVacant(3, 0, 2, 4));
+        assertFalse(grid.isRegionVacant(0, 0, 2, 1));
+    }
+
+    private GridOccupancy initGrid(int rows, int... cells) {
+        int cols = cells.length / rows;
+        int i = 0;
+        GridOccupancy grid = new GridOccupancy(cols, rows);
+        for (int y = 0; y < rows; y++) {
+            for (int x = 0; x < cols; x++) {
+                grid.cells[x][y] = cells[i] != 0;
+                i++;
+            }
+        }
+        return grid;
+    }
+}