restructure cpp headers

[ianna]

extract common code to a separate header file

[ianna]

@ManasviGoyal - FYI. When this is merged you can update your PR with:

#include "utils.h"

and remove the duplicated code from LayoutBuilder.h. Thanks!

[ManasviGoyal]

@ManasviGoyal - FYI. When this is merged you can update your PR with:

#include "utils.h"

and remove the duplicated code from LayoutBuilder.h. Thanks!

Sure. Thanks!

[codecov]

Codecov Report

Merging #1524 (8105b66) into main (0c6ae03) will decrease coverage by 2.74%.
The diff coverage is 76.88%.

Impacted Files	Coverage Δ
...awkward/_v2/_connect/rdataframe/from_rdataframe.py	0.00% <0.00%> (ø)
...c/awkward/_v2/_connect/rdataframe/to_rdataframe.py	0.00% <0.00%> (ø)
src/awkward/_v2/config.py	0.00% <0.00%> (ø)
src/awkward/_v2/types/_awkward_datashape_parser.py	47.66% <ø> (ø)
src/awkward/_v2/_connect/cling.py	25.99% <9.09%> (-0.35%)	⬇️
src/awkward/_v2/types/recordtype.py	87.06% <91.66%> (+0.83%)	⬆️
src/awkward/_v2/types/type.py	96.46% <96.10%> (-1.27%)	⬇️
src/awkward/_v2/_lookup.py	97.51% <100.00%> (+0.01%)	⬆️
src/awkward/_v2/types/__init__.py	100.00% <100.00%> (ø)
src/awkward/_v2/types/regulartype.py	90.47% <0.00%> (+4.76%)	⬆️

[jpivarski]

Moving generic things like this out to a new utils.h is a good idea.