feat: rename toXXX methods

[agoose77]

This PR tackles a small naming inconsistency. Because these are public functions, we should decide now whether to merge this!

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📚 The documentation for this PR will be available at https://awkward-array.readthedocs.io/en/agoose77-refactor-rename-to-xxx/ once Read the Docs has finished building 🔨

[agoose77]

@jpivarski I feel like we touched on this before but I don't recall the solution and can't find the discussion :/ If you're against this, close it, if in favour, merge! :)

[jpivarski]

I remember it, too. I didn't like your earlier suggestions that made the whole method names lowercase (they should reflect the names of the classes they instantiate), but I was in favor of the underscore after "to," which this PR applies.

You're right that this is our last chance to fix it because it's public API. In fact, it's public API that Uproot uses, so we'll also need to coordinate releases. It's not used by dask-awkward, awkward-pandas, or Vector, which would be harder to coordinate with.

1. I'll make a PR on Uproot that uses the new to_ names, but I will not merge it. You'll be the reviewer of that PR.
2. We'll make another pre-release of Awkward this week. (Probably more than one.)
3. Then when Uproot breaks, I'll merge that Uproot PR to unbreak it.
4. There should probably be another pre-release of Uproot, to give people something to test.

[codecov]

Codecov Report

Merging #1919 (f838754) into main (88f7fef) will not change coverage.
The diff coverage is 83.21%.

❗ Current head f838754 differs from pull request most recent head 0968729. Consider uploading reports for the commit 0968729 to get more accurate results

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/_broadcasting.py	93.38% <ø> (ø)
src/awkward/_connect/cling.py	25.40% <0.00%> (ø)
src/awkward/contents/indexedarray.py	76.60% <25.00%> (ø)
src/awkward/_util.py	82.46% <50.00%> (ø)
src/awkward/contents/bitmaskedarray.py	65.00% <59.25%> (ø)
src/awkward/contents/unmaskedarray.py	66.09% <80.00%> (ø)
src/awkward/contents/bytemaskedarray.py	87.88% <84.61%> (ø)
src/awkward/_slicing.py	86.04% <85.71%> (ø)
src/awkward/contents/numpyarray.py	89.70% <88.23%> (ø)
src/awkward/contents/regulararray.py	87.64% <92.30%> (ø)
... and 16 more

[agoose77]

I ran another test with rg "to[A-Z]" src and found a missing case.