Add compose bottom-sheet handle.

app/src/main/java/org/thoughtcrime/securesms/compose/ComposeBottomSheetDialogFragment.kt

@@ -4,10 +4,19 @@ import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
 import androidx.compose.ui.platform.ComposeView
 import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.ViewCompositionStrategy
+import androidx.compose.ui.unit.dp
 import org.signal.core.ui.theme.SignalTheme
 import org.thoughtcrime.securesms.components.FixedRoundedCornerBottomSheetDialogFragment
 import org.thoughtcrime.securesms.util.DynamicTheme
@@ -29,4 +38,29 @@ abstract class ComposeBottomSheetDialogFragment : FixedRoundedCornerBottomSheetD
 
   @Composable
   abstract fun SheetContent()
+
+  /**
+   * BottomSheet Handle, according to our design specs.
+   * This can be placed in a column with the other page content like so:
+   *
+   * ```
+   * Column(modifier = Modifier
+   *   .fillMaxWidth()
+   *   .wrapContentSize(Alignment.Center)
+   * ) {
+   *   Handle()
+   *   Text("Hello!")
+   * }
+   * ```
+   */
+  @Composable
+  fun Handle() {
+    Box(
+      modifier = Modifier
+        .size(width = 48.dp, height = 22.dp)
+        .padding(vertical = 10.dp)
+        .clip(RoundedCornerShape(1000.dp))
+        .background(MaterialTheme.colorScheme.outline)
+    )
+  }
 }