[TASK] Update bootstrap to 5.3.0-alpha3

- Drop default override styling for <hr> without classes
- Drop unused/obsolete scss variables
- Drop variable `$text-color` in favor of `$body-color`.
- Drop class `.text-muted` in favor of `.text-body-secondary`
- Drop class `.form-inline` from usage in the backend
- Icons are now displayed correctly next to text for login provider

Note: Some spacings were hotfixed for now.
It is planned to clean the `mb-*` classes up at a later point.

Resolves: #100437
Releases: main
Change-Id: I88f1d891a18acaba6a82ca498fef45b37117758e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78448


Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>