[lldb] tab completion for `target modules load -u`

1. Added a common completion ModuleUUIDs to provide a list of the UUIDs of modules for completion;
2. Added a new enumeration item eArgTypeModuleUUID to CommandArgumentType which is set as the option argument type of OptionGroupUUID;
3. Applied the module UUID completion to the argument of the type eArgTypeModuleUUID in lldb/source/Interpreter/CommandObject.cpp;
4. Added an related test case in lldb/test/API/functionalities/completion/TestCompletion.py.