Dispatch content of 4D_api.cpp into multiple .cpp files

[rouault]

No functional change, just moving code around.

4D_api.cpp has become quite large and a set of 'random' things, that didn't correlate well with the '4D' naming. Some re-organization was needed.

Create following files:

• src/area.cpp: PJ_AREA related code
• src/coordinates.cpp: functions related to coordinate manipulation
• src/coord_operation.cpp: PJCoordOperation methods
• src/create.cpp: pj_create_internal() related stuff
• src/crs_to_crs.cpp: proj_create_crs_to_crs() and the like
• src/dist.cpp: distance related functions
• src/info.cpp: proj_info() and proj_pj_info()
• src/trans.cpp: proj_trans(), proj_trans_array(), proj_trans_generic(), proj_roundtrip()
• src/trans_bounds.cpp: proj_trans_bounds()

Some other functions also moved to more relevant existing source files.

[kbevers]

This is a much needed restructuring. It's a lot simpler to navigate the code this way.

It seems all the functions in misc.cpp is related to coordinates, one way or another. Would it make sense to simply call it coordinates.cpp?

[rouault]

Would it make sense to simply call it coordinates.cpp?

I don't know. One of my initial thoughts was that it was mostly about units... But as that wasn't completely the case, I preferred misc... Not opposed to "coordinates", but I've about the same mixed feeling as "units"

[kbevers]

I'm not a massive fan of having "misc" or "utils" modules in a code base. It's never really obvious what's to be expected in them. Sometimes you really need a place to put random functions but in this case I think there is actually a common thread and the filename may as well reflect that. "coordinates" was what immediately came to my mind. There may be a better name for it.

[rouault]

Would it make sense to simply call it coordinates.cpp?

ok, I've settled on that