Control and document behavior regarding thread default bus changes depending on client bus selection strategy

With the availability of different client bus selection strategies, we need to clarify if/what changes a client construction applies to the current thread default bus.

The enforced behavior should be the following:

• THREAD_BUS strategy

     
     Bus used for client
     =======================================
     |                       | Client Bus  |
     =======================================
     |  Default  |   NULL    | New bus (Z) |
     |   Thread  |-------------------------|
     |    Bus    |   Bus X   |    Bus X    |
     =======================================
  
     State of buses before and after client creation
     =======================================
     |  Bus     |   BEFORE  |      AFTER   |
     =======================================
     |  Default |   NULL    |  New bus (Z) |
     |  Thread  |--------------------------|
     |   Bus    |   Bus X   |   Bus X      |
     =======================================
     |   TCCL   |   NULL    |    NULL      |
     |   Bus    |--------------------------|
     |          |   Bus Y   |    Bus Y     |
     =======================================
   

• NEW_BUS strategy

     
     Bus used for client
     =======================================
     |                       | Client Bus  |
     =======================================
     |  Default  |   NULL    |    New bus  |
     |   Thread  |-------------------------|
     |    Bus    |   Bus X   |    New bus  |
     =======================================
     
     State of buses before and after client creation
     =======================================
     |  Bus     |   BEFORE  |      AFTER   |
     =======================================
     |  Default |   NULL    |      NULL    |
     |  Thread  |--------------------------|
     |   Bus    |   Bus X   |      Bus X   |
     =======================================
     |   TCCL   |   NULL    |      NULL    |
     |   Bus    |--------------------------|
     |          |   Bus Y   |      Bus Y   |
     =======================================
  

• TCCL_BUS strategy

     
     Bus used for client
     =======================================
     |                       | Client Bus  |
     =======================================
     |   TCCL    |   NULL    | New bus (Z) |
     |   Bus     |-------------------------|
     |           |   Bus Y   |   Bus Y     |
     =======================================
     
     State of buses before and after client creation
     =======================================
     |  Bus     |   BEFORE  |    AFTER     |
     =======================================
     |  Default |   NULL    |    NULL      |
     |  Thread  |--------------------------|
     |   Bus    |   Bus X   |    Bus X     |
     =======================================
     |   TCCL   |   NULL    |  New bus (Z) |
     |   Bus    |--------------------------|
     |          |   Bus Y   |    Bus Y     |
     =======================================