Enable PendingJob use on Python

[sauwming]

Continuing #3774.

First of all, using PendingJob is only useful on Python.

Endpoint::utilAddPendingJob() will always execute the pending job directly unless mainThreadOnly is set to true (the default is false) (and thread count 0).

     * Utility to register a pending job to be executed by main thread.
     * If EpConfig::UaConfig::mainThreadOnly is false, the job will be
     * executed immediately.
    void utilAddPendingJob(PendingJob *job);

    /**
     * When this flag is non-zero, all callbacks that come from thread
     * other than main thread will be posted to the main thread and
     * to be executed by Endpoint::libHandleEvents() function. This
     * includes the logging callback. Note that this will only work if
     * threadCnt is set to zero and Endpoint::libHandleEvents() is
     * performed by main thread. By default, the main thread is set
     * from the thread that invoke Endpoint::libCreate()
     *
     * Default: false
     */
    bool                mainThreadOnly;

    /* See if we can execute immediately */
    if (!mainThreadOnly || pj_thread_this()==mainThread) {
        job->execute(false);
        delete job;
        return;
    }

This makes the problem much less complicated since mainThreadOnly typically won't be enabled on Java nor C# (and enabling this on Android is definitely a no no due to the main thread being the GUI thread).
Therefore, the simplest solution has been provided by @nanangizz in (#3774 (comment)) using __disown__().

This turns out to be a classical "elements within a container" problem, where we want the container to own the elements. And just for future reference, in case that we also encounter similar issues for Java and C#, the solutions are readily available in the docs:

• https://www.swig.org/Doc4.1/Java.html#Java_memory_management_objects (Memory management for objects passed to the C++ layer)
• https://www.swig.org/Doc4.1/CSharp.html#CSharp_memory_management_objects (Memory management for objects passed to the C++ layer)

For Python, the solution can be found here:

• https://www.swig.org/Doc4.1/Python.html#Python_nn35 (Ownership and object destruction)
• https://stackoverflow.com/questions/50259152/adding-swig-pythoncode-to-set-thisown-flag-on-python-object

[sauwming]

Test output:

Creating job 1
Job created id: 4312656208 value: 17136
Adding job 1
Executing job value: 17136 False
Job deleted id: 4312656208 value: 17136
Creating job 2
Job created id: 4311885776 value: 84049
Adding job 2
Collecting gc 1
Handling events
Executing job value: 84049 True
Collecting gc 2
Job deleted id: 4311885776 value: 84049

[nanangizz]

If this is only for Python, shouldn't we enable the SWIG director for Python only?
Even perhaps disable/remove the PendingJob class & utilAddPendingJob() method on other languages?