Migrate to Gradle's Plugin DSL

[HamdaanAliQuatil]

Describe the bug

Flutter has deprecated imperative apply script method to apply Gradle plugins: Deprecated imperative apply of Flutter's Gradle plugins

flutter run issues the following warning:

You are applying Flutter's app_plugin_loader Gradle plugin imperatively using the apply script method, which is deprecated and will be removed in a future release. Migrate to applying Gradle plugins with the declarative plugins block: https://flutter.dev/to/flutter-gradle-plugin-apply

You are applying Flutter's main Gradle plugin imperatively using the apply script method, which is deprecated and will be removed in a future release. Migrate to applying Gradle plugins with the declarative plugins block: https://flutter.dev/to/flutter-gradle-plugin-apply

Solution:

Migrate to Gradle plugins with the declarative plugins block.

Steps to reproduce

1. From the root of the project, execute - flutter run

Expected behavior

The warning message should not be displayed.

Screenshots

Smartphones

No response

Were you using an atApplication when the bug was found?

No response

Additional context

No response

[HamdaanAliQuatil]

@JeremyTubongbanua @TylerTrott @XavierChanth

I would love to take this up but I noticed #271 and #270 involve edits to the same files I plan to modify (though the region of intersection isn't huge)

We could either:

1. Review and merge the said PRs before we begin work on this one. Would save some trouble from rebasing later.
2. Add these edits to the same PR, perhaps by the same author. But could lead to bleeding of separate concerns and the PR already looks big to review.