DEPR: EA._pad_or_backfill not having a limit_area argument

[rhshadrach]

Ref: #56616

Currently we allow EAs to have _pad_or_backfill methods that do not accept a limit_area argument, and will only raise if e.g. Series.ffill is called with limit_area specified as either "inside" or "outside". We should deprecate this behavior, informing EA authors that override this method they need to add such an argument. The current plan:

• Add a DeprecationWarning in 3.1
• Switch to FutureWarning in 3.2
• Enforce the deprecation in 4.0