Fixes Bug #6636: AbstractControllerTestCase fails with multidimensional params array

Added test method testCanHandleMultidimensionalParams to \ZendTest\Test\PHPUnit\Controller\AbstractControllerTestCaseTest that isolates the issue
Fixed the bug by using http_build_query instead of the self-written code to generate the Request-Content
#6636 #6637 - adding `@group` annotations for newly introduced tests
Merge branch 'hotfix/#6636-#6637-abstract-controller-test-case-support-multidimensional-urlencoded-params'

Close #6636
Close #6637