DEPR/ENH: isleapyear

[jreback]

xref #13706

should deprecate pandas.util.isleapyear
and impement as an accessort to DTI, Timestamp and .dt

[jorisvandenbossche]

@jreback from #13706 (comment)

I think is_leapyear is fine

leapyear is really the common english word (I see though already getting inconsistent as we should really do is_year_leap)?

No native speaker, but the correct word is "leap year" I think? (and seems also the one most used based on google search).
If that is the case, I think is_leap_year is maybe more consistent with the other options?

[jreback]

ok that's fine (slightly inconsistent with is_year_* but oh well)