[BUGFIX] phpdoc: $urlParameters can be a string

In functions like getTypoLink() $urlParameters can also
be a string. A string is expected to be URL-encoded already,
as an array the keys are expected to be URL-encoded already
but the values not. Clearly point that out in the phpdocs.

Change-Id: Ifc767550464449fc9610f16f2e0d511b84391f60
Fixes: #44263
Releases: 4.5, 4.6, 4.7, 6.0, 6.1
Reviewed-on: https://review.typo3.org/17302
Reviewed-on: https://review.typo3.org/17304
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert