DEPR: change .astype(.., raise_on_error) -> errors

[jreback]

xref #14877

this is inconsistent with our current API handling

so need to deprecate raise_on_error, AFAICT, this is the only public use, and add
errors='raise'|'ignore', with a default a raise.

[m-charlton]

I can start to look at this one

[jreback]

sure, should be pretty straightforaward

[m-charlton]

I've noticed that the DataFrame.where method (pandas/core/internals.py) also
has a raise_on_error keyword argument. Should this be raised as a separate
issue? I can get on with the changes to astype.

[jreback]

@m-charlton yes that would be fine (you can make an issue if you want to address later). if you want to put in the same PR that is ok too. (just indicate in the top-notes that 2 things are getting deprecated)

[m-charlton]

Thinking about it, I'l raise it as a separate issue and make the changes to astype first. That
way, if I miss out anything on the deprecation of raise_on_error on astype I should not make the the same mistake on the second deprecation in the where method. When raising the new issue, I'll
link back to this one.