New reusable workflow: "find token properties"

[jrfnl]

PHP_CodeSniffer originally offered a number of "token groups" as static properties in the Tokens class to allow re-use of these groups across sniffs.
As of PHP_CodeSniffer 4.0.0, these static properties still exist, but are now (soft) deprecated in favour of class constants in the Tokens class for the same, which should create more stability, as this means the token groups can no longer be changed from within a(n external) sniff.

PHP_CodeSniffer related projects which still support both PHPCS 3.x as well as 4.x, will, for the time being, still need to use the static properties from the Tokens class.

Once a PHP_CodeSniffer related project has dropped support for PHPCS 3.x though, they can enforce the use of the class constants from the Tokens class by running this re-usable workflow in their CI.

• This workflow is particularly useful for repositories which have existing open PRs at the time of the PHPCS version drop and these open PRs should not re-introduce references to the static properties.
• This workflow can also be helpful for repositories which have contributors which contribute to a range of PHPCS related repos and for whom it would be very easy to overlook that they've used the "old-school" token group instead of the new-fangled token group constants.

In contrast to most of the other reusable workflows, this workflow does not work based on a configuration file.
One should only add a job calling this workflow to a project's CI once support for PHPCS 3.x has been dropped.

Includes adding documentation about this workflow to the README file.

[jrfnl]

Note: the "Markdown" workflow failure can be ignored - this is due to the documentation in the README file referencing the new workflow file, while that file doesn't yet exist on the main branch ;-)