fix dialog z-indexing issue

src/lib/modalPortalLayers.js

@@ -0,0 +1,65 @@
+const MODAL_PORTAL_ROOT_ID = 'vrcx-modal-portal-root';
+const APP_PORTAL_ROOT_ID = 'x-dialog-portal';
+
+const BASE_Z_INDEX = 50;
+const Z_STEP = 10;
+
+let nextLayerIndex = 0;
+
+function ensureModalPortalRoot() {
+    if (typeof document === 'undefined') {
+        return null;
+    }
+
+    let root = document.getElementById(APP_PORTAL_ROOT_ID);
+    if (root) {
+        root.style.position ||= 'relative';
+        root.style.isolation ||= 'isolate';
+        return root;
+    }
+
+    root = document.getElementById(MODAL_PORTAL_ROOT_ID);
+    if (root) {
+        return root;
+    }
+
+    root = document.createElement('div');
+    root.id = MODAL_PORTAL_ROOT_ID;
+    root.style.position = 'relative';
+    root.style.isolation = 'isolate';
+    document.body.appendChild(root);
+    return root;
+}
+
+export function acquireModalPortalLayer() {
+    const root = ensureModalPortalRoot();
+    if (!root) {
+        return {
+            element: undefined,
+            bringToFront() {},
+            release() {}
+        };
+    }
+
+    const element = document.createElement('div');
+    element.dataset.vrcxPortalLayer = 'modal';
+    element.style.position = 'relative';
+    element.style.isolation = 'isolate';
+    root.appendChild(element);
+
+    const bringToFront = () => {
+        nextLayerIndex += 1;
+        element.style.zIndex = String(BASE_Z_INDEX + nextLayerIndex * Z_STEP);
+        root.appendChild(element);
+    };
+
+    const release = () => {
+        element.remove();
+    };
+
+    return {
+        element,
+        bringToFront,
+        release
+    };
+}