Split unit and benchmark tests in QtBase

Move benchmark tests code to test/benchmarks/* for:

• tests/auto/sql/kernel/qsqlquery/tst_qsqlquery.cpp
• tests/auto/corelib/tools/qcontiguouscache/tst_qcontiguouscache.cpp

These selftests seem to be ok.

• tests/auto/testlib/selftests/badxml/tst_badxml.cpp
• tests/auto/testlib/selftests/benchlibwalltime/tst_benchlibwalltime.cpp
• tests/auto/testlib/selftests/benchlibtickcounter/tst_benchlibtickcounter.cpp
• tests/auto/testlib/selftests/benchlibeventcounter/tst_benchlibeventcounter.cpp
• tests/auto/testlib/selftests/benchlibcallgrind/tst_benchlibcallgrind.cpp
• tests/auto/testlib/selftests/benchliboptions/tst_benchliboptions.cpp