[DOCS] Use "Bootstrap" instead of "Twitter Bootstrap" in EXT:form documentation

Twitter made the CSS framework Open Source in 2011, since then it is called only "Bootstrap".

Resolves: #101840
Releases: main, 12.4, 11.5
Change-Id: I05c7d9ce3a197cb61058a5582918935d6720e371
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80838


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>