API: Add reduction methods to ExtensionArray subclasses #64450
Description
The subclasses of ExtensionArray implemented within pandas can support various reductions, but many do not have specific reduction methods defined, e.g. .mean(). We should fill these out for better API consistency.
The only method that should be added to ExtensionArray itself is count, as this can be implemented for all EAs via ExtensionArray.isna.
I'm already working on this.