Fix debug command in nomultiline mode

[tompng]

Fixes #909 and #1003

Fix this bug

% irb --readline
irb(main):001> binding.irb
irb(main):001> debug
/Users/tomoya.ishida/.rbenv/versions/3.3.1/lib/ruby/gems/3.3.0/gems/irb-1.14.0/lib/irb/debug.rb:72:in `block in setup': undefined method `call' for nil (NoMethodError)

            irb_output_modifier_proc.call(output, complete: complete)
                                    ^^^^^

rendering test conflicts with #1001

[st0012]

I feel colorize_input express the intent better and is less likely to be confused with Color.colorize_code?

[tompng]

It looks better, but I have one concern. colorize_input colorizes output. I think it is an input, but Reline's api calls it output.
Do you think the code below is acceptable? IMO... maybe yes?

Reline.output_modifier_proc = proc do |output, complete:|
  IRB.CurrentContext.colorize_input(output, complete: complete)
end

[st0012]

In IRB's context, it is input indeed. And in Reline's context, I think calling it both input or output are technically correct? Though since there's no input_modifier_proc, I feel it'd be a better name for the library user's perspective.

In this case, I feel a comment to clarify it would be enough, and maybe rename the output variable to input?

[st0012]

Thank you!