'behaviorof' should take Array, not layouts, and setting 'behavior' should set the '__class__'.

[jpivarski]

• Also, all of the other uses of ak._util.behaviorof that are being passed layouts, rather than ak.Array wrappers (which is the level that could possibly have behaviors).

[codecov]

Codecov Report

Merging #1153 (daf4fbf) into main (f795658) will increase coverage by 0.34%.
The diff coverage is 77.83%.

Impacted Files	Coverage Δ
src/awkward/_v2/forms/bitmaskedform.py	75.64% <ø> (ø)
src/awkward/_v2/forms/bytemaskedform.py	76.05% <ø> (ø)
src/awkward/_v2/forms/emptyform.py	76.92% <ø> (ø)
src/awkward/_v2/forms/indexedoptionform.py	76.81% <ø> (ø)
src/awkward/_v2/forms/listform.py	75.94% <ø> (ø)
src/awkward/_v2/forms/listoffsetform.py	80.55% <ø> (ø)
src/awkward/_v2/forms/recordform.py	66.46% <ø> (ø)
src/awkward/_v2/forms/regularform.py	75.34% <ø> (ø)
src/awkward/_v2/forms/unionform.py	76.19% <ø> (ø)
src/awkward/_v2/forms/unmaskedform.py	74.57% <ø> (ø)
... and 52 more