[TASK] Avoid implicitly nullable parameter on `DatabaseRecordException`

With PHP 8.4 marking method parameter implicitly nullable
is depreacted and will emit a `E_DEPRECATED` warning. One
recommended way to resolve this, is making it explicitly
nullable using the `?` nullable operator. [1]

In cases, where are implicitly nullable parameter exists
before not-nullable parameters in a method or constructor,
making it explicitly nullable will emit a

  Optional parameter <paramname> declared before required
  parameter <paramname> is implicitly treated as a required
  parameter

since PHP 8.0 [2].

This change removes the `null` default value and adds the `?`
nullable operator to the previousException parameter for the
`\TYPO3\CMS\Backend\Form\Exception\DatabaseRecordException`
constructor.

This prepares the way towards PHP 8.4 compatibility.

[1] https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated
[2] https://php.watch/versions/8.0/deprecate-required-param-after-optional

Resolves: #103926
Releases: main, 12.4, 11.5
Change-Id: I4d1506b24b3113a74b37b986fa4f23f24e6219fb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84415


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>