SessionIOJSON: add the create method

MSVC complains about it. It is used, so why GCC and Clang are happy is a
different story.
Status Job ID Name Coverage
  External
passed cdash

passed kwrobot-branch-check

passed smtk-endor-linux-shared-relwithdebinfo

passed smtk-endor-linux-shared-relwithdebinfo

passed smtk-endor-linux-shared-relwithdebinfo

passed smtk-endor-linux-shared-relwithdebinfo

passed smtk-endor-linux-shared-relwithdebinfo

passed smtk-endor-linux-shared-relwithdebinfo

passed smtk-endor-linux-shared-relwithdebinfo

00:02:23