[BUGFIX] Use current site language in indexed search by default

Using Indexed Search plugin, one can customize the language selector,
however, you needed a TypoScript condition, as Site Handling support
was not possible yet.

The default behaviour should be to only search in the selected language,
which can be achieved by looking into the current language.

The default option is now set to "current". Existing implementations
still using conditions continue to keep working.

Resolves: #80840
Releases: master, 9.5
Change-Id: I7772e40d11593331cddf8fc90c8630f0a4db1758
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62382


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Gorges <daniel.gorges@b13.com>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Daniel Gorges <daniel.gorges@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Susanne Moog <look@susi.dev>