Add "Themed Icons" for Android

[rileychh]

Description

This PR adds support for Themed Icons on Android. This feature allows users running Android 13 or later theme our app icon based on the system theme.

Implementation

• Re-enable flutter_launcher_icons with the version added support for themed icons.
• Add android.png with the background removed as the foreground for the adaptive icon.
• Rename tat.png to original.png, and use this image for iOS and older Android versions.

Testing Instructions

Install the app on Android, drag a shortcut onto the home screen, and enable "Themed Icons" in the launcher settings. Verify that the TAT logo correctly follows the system theme.

Additional Notes

N/A.

[rileychh]

Just found out that the flutter_launcher_icons we use has added support for themed icons in a merged PR. Should we use this tool to generate these icons instead?

edit: to use this unreleased feature, we need to switch to the latest master version.

[rileychh]

Re-implemented with flutter_launcher_icons. Please review again.

[rileychh]

Please note that this PR is blocked by #224. Without a proper splash screen for Android 12 and later, the app will launch with 2 splash screens.

Demonstration:

Details about double splash screen: https://stackoverflow.com/questions/77098464/play-console-pre-launch-warning-double-splash-screen