[TASK] IndexedSearch: Extract enum-esque structs into real enums

IndexedSearch uses a bunch of "randomly" defined values for options that
are hard to read and understand in the code flow. To improve the
situation a bit, such structs are now converted into real PHP enums,
providing assistance when reading and/or refactoring code.

Resolves: #102898
Releases: main
Change-Id: I1eac6344485a464ac2ad1e53a948a6ebc5e182cd
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82598


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>