Local error handlers for application commands

[izxxr]

Summary

Add support for local error handlers for application commands.

What is the feature request for?

The core library

The Problem

Application commands don't support local error handlers.

The Ideal Solution

Implement local error handlers for application commands in manner similar to ext.commands, as such;

@bot.slash_command()
async def slash(ctx):
  ...

@slash.error
async def on_slash_error(ctx, error):
  ...

The Current Solution

No response

Additional Context

No response