C++ refactoring: getting Numba to work for v2 arrays

[jpivarski]

Tests of Numba to convert:

• test_0056b-partitioned-array-numba.py no more partitioned arrays
• test_0057b-virtual-array-numba.py no more virtual arrays
• test_0124-strings-in-numba.py
• test_0127b-tomask-operation-numba.py
• test_0290-bug-fixes-for-hats.py
• test_0390-virtual-forms.py no more virtual arrays
• test_0395-fix-numba-indexedarray.py
• test_0494-numba-array-contains.py
• test_0549-numba-array-asarray.py
• test_0559-fix-booleans-in-numba.py
• test_0572-numba-array-ndim.py
• test_0776-numba-booleans-in-virtual-array.py no more virtual arrays
• test_0871-nested-virtual-in-numba.py no more virtual arrays
• test_0903-ArrayView-expects-contiguous-NumpyArrays.py

Need to implement ArrayBuilder in Numba for these:

• test_0118-numba-cpointers.py
• test_0397-arrays-as-constants-in-numba.py

Need to implement matrix multiplication for these (another PR):

• test_0521-matrix-multiplication.py
• test_0846-matrix-multiplication-numpy.py

[codecov]

Codecov Report

Merging #1240 (06b933e) into main (8e68200) will increase coverage by 1.70%.
The diff coverage is 79.39%.

Impacted Files	Coverage Δ
src/awkward/_v2/_connect/numba/arrayview.py	96.24% <ø> (ø)
src/awkward/_v2/_connect/numba/layout.py	87.01% <ø> (ø)
src/awkward/_v2/contents/bytemaskedarray.py	81.09% <9.09%> (-1.96%)	⬇️
src/awkward/_v2/contents/indexedarray.py	59.17% <10.00%> (-1.47%)	⬇️
src/awkward/_v2/contents/unmaskedarray.py	55.25% <20.00%> (-0.83%)	⬇️
src/awkward/_v2/operations/io/ak_to_json_file.py	47.05% <43.75%> (-27.95%)	⬇️
src/awkward/_v2/contents/emptyarray.py	69.14% <50.00%> (-0.23%)	⬇️
src/awkward/_v2/forms/emptyform.py	77.35% <50.00%> (-1.08%)	⬇️
src/awkward/_v2/contents/content.py	81.59% <58.33%> (-0.47%)	⬇️
src/awkward/_v2/contents/regulararray.py	81.97% <58.82%> (-0.88%)	⬇️
... and 37 more