deps: Upgrade Flutter to latest main, 3.12.0-7.0.pre.54

And update Flutter's supporting libraries to match,
namely adding package:web.

Author: gnprice

pubspec.lock

@@ -933,6 +933,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.1.0"
+  web:
+    dependency: transitive
+    description:
+      name: web
+      sha256: dc8ccd225a2005c1be616fe02951e2e342092edf968cf0844220383757ef8f10
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.1.4-beta"
   web_socket_channel:
     dependency: transitive
     description:
@@ -982,5 +990,5 @@ packages:
     source: hosted
     version: "3.1.2"
 sdks:
-  dart: ">=3.1.0-163.0.dev <4.0.0"
-  flutter: ">=3.11.0-18.0.pre.81"
+  dart: ">=3.1.0-236.0.dev <4.0.0"
+  flutter: ">=3.12.0-7.0.pre.54"

pubspec.yaml

@@ -24,8 +24,8 @@ environment:
   # that by the time we want to release, these will have become stable.
   # TODO: Before general release, switch to stable Flutter and Dart versions,
   #   or pin exact versions: https://github.com/zulip/zulip-flutter/issues/15
-  sdk: '>=3.1.0-163.0.dev <4.0.0'
-  flutter: '>=3.11.0-18.0.pre.81'
+  sdk: '>=3.1.0-236.0.dev <4.0.0'
+  flutter: '>=3.12.0-7.0.pre.54'
 
 # Dependencies specify other packages that your package needs in order to work.
 # To automatically upgrade your package dependencies to the latest versions