[file_selector_web] migrate to pkg:web (#5413)

This allows this package to be used in a web app compiled to Wasm.

Helps unblock https://github.com/flutter/devtools/issues/6606

script/configs/allowed_unpinned_deps.yaml

@@ -51,6 +51,7 @@
 - test_api
 - vm_service
 - wasm
+- web
 - yaml
 # Google-owned packages
 - _discoveryapis_commons

script/tool/lib/src/common/core.dart

@@ -68,6 +68,7 @@ final Map<Version, Version> _dartSdkForFlutterSdk = <Version, Version>{
   Version(3, 10, 0): Version(3, 0, 0),
   Version(3, 10, 6): Version(3, 0, 6),
   Version(3, 13, 0): Version(3, 1, 0),
+  Version(3, 16, 0): Version(3, 2, 0),
 };
 
 /// Returns the version of the Dart SDK that shipped with the given Flutter