[BUGFIX] Allow custom AbortSignal to be passed to AjaxRequest methods

AjaxRequest uses an own AbortController instance in order to provide
the abort() method. It therefore passes the corresponding AbortSignal
instance as a forced option to fetch(), and overwrites any custom
signal that is passed as request options.

In order to support custom AbortSignal's passed as fetch option,
the abort event of the custom AbortSignal is now forwarded to the
internal AbortController instance.

Resolves: #102286
Releases: main, 12.4
Change-Id: I8011c1794acc22a6d9d2e874a02c1a8c97e532dc
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81613


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>