[BUGFIX] Make Extbase Cli\RequestBuilder a Singleton

Like the Web\RequestBuilder the Cli\RequestBuilder is a service
object for the RequestHandler. It gets injected and has no
internal state, thus it should be a Singleton.

Resolves: #57591
Releases: 6.2
Change-Id: I959fcfdbc4182cd86cd38d438a0ff7f0de1845f1
Reviewed-on: https://review.typo3.org/29112
Reviewed-by: Wouter Wolters
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind