Migrate apple-mobile-web-* to mobile-web-*. (#154964)

Closes https://github.com/flutter/flutter/issues/154596.

It's less clear to me if your goal was to migrate _all_ of these btw:
https://github.com/search?q=org%3Aflutter+%22mobile-web-app-capable%22&type=code

examples/api/web/index.html

@@ -24,7 +24,7 @@ found in the LICENSE file. -->
   <meta name="description" content="A temporary code sample for Curve2D">
 
   <!-- iOS meta tags & icons -->
-  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="mobile-web-app-capable" content="yes">
   <meta name="apple-mobile-web-app-status-bar-style" content="black">
   <meta name="apple-mobile-web-app-title" content="flutter_api_samples">
   <link rel="apple-touch-icon" href="icons/Icon-192.png">