Resolve #3148506 "Cumulative d9 compatibility"

Cumulative Drupal 9 Compatibility Fixes.

This MR combines all the Drupal 9 compatibility patches from https://www.drupal.org/project/progress_bar/issues/3148506#comment-14041451 and adds a valid composer.json to the repository, so that the issue fork can be used as a Composer repository for a D8/D9 transitional package.

The description from entity_activity!3 continues unedited (except for name of git feature branch) below:

It is useful to have an issue fork for Drupal 9 compatibility, rather than simply a patch, because:

In short, you can't use a patch to tell Composer that a Drupal 8 module is compatible with Drupal 9.

Source: https://www.mediacurrent.com/blog/how-fix-catch-22-problem-drupal-9-fixes-composer/

Adding Issue Fork as a Composer repository:

To use this issue fork as a transitional D9-compatible package in your project, modify your composer.json:

    "repositories": {
        "drupal/progress_bar": {
            "type": "vcs",
            "url": "https://git.drupalcode.org/issue/progress_bar-3148506"
        },
        "drupal": {
          "type": "composer",
          "url": "https://packages.drupal.org/8",
          "exclude": ["drupal/progress_bar"]
        },

Requiring the patched package from the Issue Fork:

Execute the following command in a terminal:

$ composer require drupal/progress_bar:dev-3148506-cumulative-d9-compatibility

or manually add the requirement to composer.json:

    "require": {
        "drupal/progress_bar": "dev-3148506-cumulative-d9-compatibility",

Credit due, mainly, to Benji Fisher via: https://www.drupal.org/project/views_url_alias/issues/3142138#comment-14177409

NOTE: Tested with Drupal 8. Transitional module now passes Upgrade Status D9 compatibility test.

NOTE: Not yet tested with Drupal 9. You can help the Drupal community by testing this! 👍

Closes #3148506