Backend module: add display for percentage of finished tests

Ticket on Forge: https://forge.typo3.org/issues/50456

Author: Peter Kraume

Description:

Especially the link test can have thousands of single tests. So it would be useful to see how many of the tests have already been done. Even cooler would be a display like this:

Total Tests: X Checked: X% Errors: X Warnings: X Success: X

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