[TASK] Declare getThisScript() in ElementBrowser as public

To make work in hooks easier, the method should be public

Resolves: #56721
Releases: 6.2
Change-Id: Ib0a0f17d5f9384a04a125ef08a079f4c272eddae
Reviewed-on: https://review.typo3.org/28337
Reviewed-by: Alexander Stehlik
Tested-by: Alexander Stehlik
Reviewed-by: Markus Klein
Tested-by: Markus Klein