[DevTools] Fix Flow type errors for TraceUpdates popover implementation

  Added $FlowFixMe annotations to address Flow type errors with the Popover API:

  - prop-missing: Added annotations for Popover API methods (showPopover, hidePopover)
    that Flow doesn't yet recognize in HTMLCanvasElement
  - incompatible-use: Fixed type errors related to null checking and property access

  Flow doesn't have built-in types for the new Popover API yet, so we need to
  tell it to ignore these specific errors while maintaining type safety
  for the rest of the codebase.

Author: yongsk0066

packages/react-devtools-shared/src/backend/views/TraceUpdates/canvas.js

@@ -28,6 +28,7 @@ const COLORS = [
   '#febc38',
 ];
 
+// $FlowFixMe[prop-missing] - Flow doesn't know about Popover API methods
 let canvas: HTMLCanvasElement | null = null;
 
 function drawNative(nodeToData: Map<HostInstance, Data>, agent: Agent) {
@@ -47,7 +48,9 @@ function drawWeb(nodeToData: Map<HostInstance, Data>) {
   if (nodeToData.size === 0) {
     if (canvas !== null) {
       try {
+        // $FlowFixMe[incompatible-use] - Flow doesn't know about Popover API
         if (canvas.matches(':popover-open')) {
+          // $FlowFixMe[prop-missing]
           canvas.hidePopover();
         }
       } catch (e) {}
@@ -59,7 +62,9 @@ function drawWeb(nodeToData: Map<HostInstance, Data>) {
     initialize();
   } else {
     try {
+      // $FlowFixMe[incompatible-use]
       if (!canvas.matches(':popover-open')) {
+        // $FlowFixMe[prop-missing]
         canvas.showPopover();
       }
     } catch (e) {}
@@ -209,8 +214,12 @@ function destroyNative(agent: Agent) {
 
 function destroyWeb() {
   if (canvas !== null) {
-    canvas.hidePopover();
+    try {
+      // $FlowFixMe[prop-missing]
+      canvas.hidePopover();
+    } catch (e) {}
 
+    // $FlowFixMe[incompatible-use]
     if (canvas.parentNode != null) {
       canvas.parentNode.removeChild(canvas);
     }
@@ -226,6 +235,7 @@ function initialize(): void {
   canvas = window.document.createElement('canvas');
   canvas.setAttribute('popover', 'manual');
 
+  // $FlowFixMe[incompatible-use]
   canvas.style.cssText = `
     xx-background-color: red;
     xx-opacity: 0.5;
@@ -236,15 +246,16 @@ function initialize(): void {
     right: 0;
     top: 0;
     background-color: transparent;
-    outline: none !important;
-    box-shadow: none !important;
-    border: none !important;
+    outline: none;
+    box-shadow: none;
+    border: none;
   `;
 
   const root = window.document.documentElement;
   root.insertBefore(canvas, root.firstChild);
 
   try {
+    // $FlowFixMe[prop-missing]
     canvas.showPopover();
   } catch (e) {}
 }