Gradle 6.5 - "Could not find method leftShift()"

# Bug Report
gradle.extras fail with gradle 6.5

## Problem
When using gradle 6.5 to build a cordova Android app, the build crashes with the following error:
> "A problem occurred evaluating project ':app'.
> Could not find method leftShift() for arguments [build_extras_iirp9rj48r4etl69rhtwhtw1$_run_closure1$_closure2@49b383e8] > on task ':app:cdvCreateAssetManifest' of type org.gradle.api.DefaultTask."

### What is expected to happen?
It is expected to build without issues.

### What does actually happen?
See problem.

## Information
This seems to relate to the fact that the << - notation is deprecated in newer gradle versions.
https://stackoverflow.com/questions/55793095/could-not-find-method-leftshift-for-arguments-after-updating-studio-3-4

### Command or Code
building a cordova app to Android

### Environment, Platform, Device
Fresh installed Ubuntu with the Angular/Cordova stack.

### Version information
Angular: 10.0.14
Cordova: 10
cordova-plugin-file: 6.0.2
Gradle 6.5

## Checklist

- [x] I searched for existing GitHub issues
- [x] I updated all Cordova tooling to most recent version
- [x] I included all the necessary information above

Start from the Cordova Android build extras that invoke Gradle's deprecated leftShift()/<< notation, using the linked Stack Overflow report for context. Reproduce the failure by building an Angular/Cordova app with Gradle 6.5, and consider the work done when the app builds without the cdvCreateAssetManifest error.

Written by the indexing model from the issue text.