Diagnostics: reduce reliance on WarpX::GetInstance()

[lucafedeli88]

Reduce reliance on WarpX::GetInstance() in diagnostics by passing more parameters as arguments.

What do you think about passing a group of parameters as a struct?

struct InitDiagnosticsParameters
{
    int finest_level;
    int max_level;

    int do_moving_window;
    int moving_window_dir;
    amrex::Real moving_window_x;
    amrex::Real cell_size_lev0_mwdir;
};

I think that it is useful especially for WarpXIO.cpp since several function calls requiring these parameters are made.
I am really sorry that C++17 doesn't have label initialization for structs like C .

⚠️⚠️ ⚠️ Note that FlushFormatSensei requires a pointer to the base class of the WarpX object, which is now passed as an argument auto* p_warpx_mesh = dynamic_cast<amrex::AmrMesh*>(this); . Before, this was obtained by const casting a const pointer obtained from WarpX::GetInstance(). The refactored code has the added benefit that it removes this const_cast (usage of const_cast is often discouraged because it could lead to Undefined Behavior issues, see: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#es50-dont-cast-away-const).