add jsonpickle and pexpect libs in case of unsafe decoding and secondary command execution, add proper test cases

python/ql/test/library-tests/frameworks/pexpect/ConceptsTest.expected

@@ -0,0 +1,2 @@
+testFailures
+failures

python/ql/test/library-tests/frameworks/pexpect/ConceptsTest.ql

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+import python
+import experimental.meta.ConceptsTest

python/ql/test/library-tests/frameworks/pexpect/ExecCmd.py

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+import pexpect
+from pexpect import popen_spawn
+
+cmd = "ls -la"
+result = pexpect.run(cmd) # $ getCommand=cmd
+result = pexpect.runu(cmd) # $ getCommand=cmd
+result = pexpect.spawn(cmd) # $ getCommand=cmd
+result = pexpect.spawnu(cmd) # $ getCommand=cmd
+result = popen_spawn.PopenSpawn(cmd) # $ getCommand=cmd