Fix operationAsString Export

[ax3l]

The operationAsString function is used in the ADIOS1 backend, which does symbol hiding to wrap ADIOS1's MPI mock library. Thus, we need to export this symbol once we wrap ADIOS1.

Fix #1308

[ax3l]

Interesting, had a flake in Tooling / Clang ASAN USBSAN:

number of particle species: 0
[AbstractIOHandlerImpl] IO Task OPEN_FILE failed with exception. Removing task from IO queue and passing on the exception.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SerialIOTests is a Catch v2.13.9 host application.
Run with -? for options

-------------------------------------------------------------------------------
append_mode
-------------------------------------------------------------------------------
/home/runner/work/openPMD-api/openPMD-api/test/SerialIOTest.cpp:6108
...............................................................................

/home/runner/work/openPMD-api/openPMD-api/test/SerialIOTest.cpp:6108: FAILED:
  {Unknown expression after the reported line}
due to unexpected exception with message:
  ERROR: attribute /date has been defined and its value cannot be changed, in
  call to DefineAttribute

will restart.

[franzpoeschel]

Interesting, had a flake in Tooling / Clang ASAN USBSAN:

number of particle species: 0
[AbstractIOHandlerImpl] IO Task OPEN_FILE failed with exception. Removing task from IO queue and passing on the exception.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SerialIOTests is a Catch v2.13.9 host application.
Run with -? for options

-------------------------------------------------------------------------------
append_mode
-------------------------------------------------------------------------------
/home/runner/work/openPMD-api/openPMD-api/test/SerialIOTest.cpp:6108
...............................................................................

/home/runner/work/openPMD-api/openPMD-api/test/SerialIOTest.cpp:6108: FAILED:
  {Unknown expression after the reported line}
due to unexpected exception with message:
  ERROR: attribute /date has been defined and its value cannot be changed, in
  call to DefineAttribute

will restart.

This is a bug on dev in combination with ADIOS2 v2.7, #1302 will fix it