Optimize Synchronization of Nodal Points

[EZoni]

Here's a few points that need to be addressed in order to optimize the synchronization of nodal points in WarpX:

• Merge synchronization of nodal points into FillBoundary:
  • OneStep_nosub
    PR: Merge FillBoundary and NodalSync (OneStep_nosub, OneStep_sub1) #3013
  • OneStep_sub1
    PR: Merge FillBoundary and NodalSync (OneStep_nosub, OneStep_sub1) #3013
  • OneStep_multiJ
    PR: Merge FillBoundary and NodalSync (OneStep_multiJ) #3169
• Merge and move synchronization of nodal points for PML fields as well
  PR: Merge nodal synchronization with FillBoundary calls in PML #3534
• Check if we can remove the synchronization of nodal points in J/rho (historically, we first implemented the synchronization of J/rho, and then that of E/B: Add nodal synchronization of E and B fields in the main grid #1817. However, after adding the synchronization of E/B, intuitively it seems that synchronizing J/rho is not needed anymore.)
  PR: Remove Nodal Synchronization of J and Rho #3038
• Clean up or remove the functions NodalSync
  PR: Merge FillBoundary and NodalSync (OneStep_multiJ) #3169