deps: Add convert as a direct dependency

We expect to use this in the OTP protocol in web auth (zulip#281).

Author: chrisbobbe

pubspec.lock

@@ -202,7 +202,7 @@ packages:
     source: hosted
     version: "1.3.3"
   convert:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: convert
       sha256: "0f08b14755d163f6e2134cb58222dd25ea2a2ee8a195e53983d57c075324d592"

pubspec.yaml

@@ -58,6 +58,7 @@ dependencies:
   package_info_plus: ^5.0.1
   collection: ^1.17.2
   url_launcher: ^6.1.11
+  convert: ^3.1.1
   url_launcher_android: ">=6.1.0"
   flutter_localizations:
     sdk: flutter