Modify send_data_3d in diag_manager.F90 to move SELECT TYPE blocks out of triple do loops

[MinsukJi-NOAA]

Regarding this PR, the following tests have been conducted:

• CI tests (with GNU) all passed.
• cpld_control_p7 test on Hera
  • With 64 bit dycore and 64 bit FMS, results reproduce the baseline
  • With 32 bit dycore and 64 bit FMS, results do not reproduce the baseline
  • As a side note, the test with 32 bit dycore runs 15% faster than that with 64 bit dycore
• control test on Hera
  • With 32 bit dycore and 64 bit FMS, results do not reproduce the baseline
  • With 32 bit dycore and 32 bit FMS, results reproduce the baseline

[junwang-noaa]

So the 32bit fv3 with 32bit fms reproduces current results, that's great!