[!!!][BUGFIX] Make indexed search plugin PHP7 compatible

Rename SearchFormController::pi_list_browseresults as it had different
signature than defined in parent AbstractPlugin and there is no
non breaking way to make it PHP7 compatible.

Resolves: #72931
Releases: 7.6, master
Change-Id: I3dc36386a3866b5ca87d48d2869c21b9a37fbfe3
Reviewed-on: https://review.typo3.org/47349


Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>