Deprecated Java 8 warnings

[OutdatedGuy]

Java 8 was deprecated with the release of Android Studio Ladybug, and is set to be removed in an upcoming version.

All Flutter's 1st party plugins have migrated to Java 11 now.

Reproduce Steps

Steps to reproduce the behavior:

1. Run any example of any plugin on Android in debug mode
2. See warnings:

   warning: [options] source value 8 is obsolete and will be removed in a future release
   warning: [options] target value 8 is obsolete and will be removed in a future release

Expected behavior

No warnings should be printed.

Version (please complete the following information):

• Flutter Version: 3.29.3
• OS: Android
• plugin: All plugins