Fix Sheet native blocking issue on iOS and cleanup logic.

1. Refine blocker identification using a client property to avoid accidental removal of other components.
2. Update KotlinUiTest.kt and BrowserComponentScreenshotTest.java to use sheet.show(0) to prevent potential animation-related hangs on iOS.
3. Verify core logic with SheetPeerBlockingTest.

Author: google-labs-jules[bot]

CodenameOne/src/com/codename1/ui/Sheet.java

@@ -483,7 +483,7 @@ public void paint(Graphics g, Rectangle rect) {
         for (Component child : cnt) {
             if (child instanceof Sheet) {
                 foundSheet = true;
-            } else {
+            } else if (Boolean.TRUE.equals(child.getClientProperty("SheetBlocker"))) {
                 blocker = child;
             }
         }
@@ -492,6 +492,7 @@ public void paint(Graphics g, Rectangle rect) {
         if (needsBlocker) {
             if (blocker == null) {
                 blocker = new Button();
+                blocker.putClientProperty("SheetBlocker", Boolean.TRUE);
                 blocker.setUIID("Container");
                 blocker.getAllStyles().setBgTransparency(0);
                 blocker.setPreferredSize(new com.codename1.ui.geom.Dimension(10000, 10000));

scripts/hellocodenameone/common/src/main/java/com/codenameone/examples/hellocodenameone/tests/BrowserComponentScreenshotTest.java

@@ -60,7 +60,7 @@ public void onSucess(BrowserComponent.JSRef result) {
 
         Sheet sheet = new Sheet(null, "Overlay Sheet");
         sheet.getContentPane().add(new Label("This is a sheet covering part of the browser"));
-        sheet.show();
+        sheet.show(0);
 
         UITimer.timer(2000, false, form, readyRunnable);
         readyRunnable = null;

scripts/hellocodenameone/common/src/main/kotlin/com/codenameone/examples/hellocodenameone/tests/KotlinUiTest.kt

@@ -55,7 +55,7 @@ class KotlinUiTest : BaseTest() {
 
         val sheet = Sheet(null, "Overlay Sheet")
         sheet.contentPane.add(Label("This is a sheet covering part of the screen"))
-        sheet.show()
+        sheet.show(0)
 
         return true
     }