Can't use IRB when FakeFS is activated

[mrzasa]

IRB can't start when FakeFS is activated, because it can't open the history file.

See the minimal example below:

require 'fakefs'

RSpec.describe 'IRB inside FakeFS' do
  it 'works' do
    binding.irb
  end
end

it ends up with an error:

    Failure/Error: Unable to find pry-fakefs/irb_spec.rb to read failed line
     
     Errno::ENOENT:
       No such file or directory - /home/mrzasa/.irb-history
     # ruby-3.0.4/gems/fakefs-1.8.0/lib/fakefs/file.rb:876:in `check_file_existence!'
     # ruby-3.0.4/gems/fakefs-1.8.0/lib/fakefs/file.rb:503:in `initialize'
     # ruby-3.0.4/gems/fakefs-1.8.0/lib/fakefs/kernel.rb:40:in `open'
     # ruby-3.0.4/gems/fakefs-1.8.0/lib/fakefs/kernel.rb:40:in `block in <module:Kernel>'
     # pry-fakefs/irb_spec.rb:5:in `block (2 levels) in <top (required)>'

This I believe is an effect of hijacking the Kernel#open method. To fix it we need to unhijack it in the IRB context.

Related to #290

Similar issue with pry is addressed in this PR: #485 (the pry problem is simpler though - it's enough to assign correctly mocked classes).

[grosser]

PR welcome