Review qtgrpc/src

Review all source code and header files in the Qt source code sub directory mentioned in the summary of this task. Marking this task as done implies that every file was reviewed and assessed for its criticality according to QUIP 23.  Alternatively if no file was marked, it implies that no code section was deemed to be critical from a security perspective.

For more context information about this task please check the description of the epic associated with this task.

More information: https://contribute.qt-project.org/quips/23