Add support for Node#obscured?

[myabc]

This PR adds initial support for Node#obscured?.

Enables the obscured: option with Capybara::Node::Finders#all, Capybara::Node::Finders#find and the various assertion methods and matchers that support the same options, e.g.

      assert_selector("button[data-close-dialog-id]", obscured: false)
      assert_selector("button[data-submit-dialog-id]", obscured: false)

Essentially it is a port of Capybara::Selenium::Node#obscured? including the injected script (Capybara::Selenium::Node::OBSCURED_OR_OFFSET_SCRIPT).

A couple things to note:

• This PR also includes Skip injecting extensions on frame switch to prevent javascript errors #201 - albeit with one small fix. Without it I'm seeing a undefined method execution_id!' for nil` error (details below).
• I struggled with the fact that a Ferrum::Frame is not a Ferrum::Node - in the Selenium implementation, frames are Capybara::Node::Element. The code that gets the corresponding iframe Node for a given frame is hacky - ideally Ferrum::Frame would provided a #to_node node or similar.
• There is now an upstream PR implementing Ferrum::Frame#node: feat: Add Frame#frame_element method ferrum#524 - This PR isn't dependent on the upstream PR being merged, but it could easily be adapted.

---

undefined method `execution_id!' for nil stack trace

  1) Capybara::Session Cuprite node #obscured? should work in nested iframes
     Failure/Error: inject_extensions
 NoMethodError:
   undefined method `execution_id!' for nil
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/ferrum-0.16/lib/ferrum/page.rb:490:in `block in inject_extensions'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/ferrum-0.16/lib/ferrum/page.rb:483:in `each'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/ferrum-0.16/lib/ferrum/page.rb:483:in `inject_extensions'
 # ./lib/capybara/cuprite/page.rb:126:in `switch_to_frame'
 # ./lib/capybara/cuprite/browser.rb:284:in `frame_obscured_at?'
 # ./lib/capybara/cuprite/browser.rb:221:in `obscured?'
 # ./lib/capybara/cuprite/node.rb:21:in `command'
 # ./lib/capybara/cuprite/node.rb:217:in `obscured?'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/node/element.rb:317:in `block in obscured?'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/node/base.rb:84:in `synchronize'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/node/element.rb:317:in `obscured?'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/spec/session/node_spec.rb:358:in `block (6 levels) in <top (required)>'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/session.rb:451:in `within_frame'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/spec/session/node_spec.rb:357:in `block (5 levels) in <top (required)>'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/session.rb:451:in `within_frame'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/spec/session/node_spec.rb:355:in `block (4 levels) in <top (required)>'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/session.rb:451:in `within_frame'
 # /Users/alexbcoles/.gem/ruby/3.3.4/gems/capybara-3.40.0/lib/capybara/spec/session/node_spec.rb:354:in `block (3 levels) in <top (required)>'
 # ./spec/spec_helper.rb:109:in `block (2 levels) in <top (required)>'

[toy]

I don't see anything suspicious, but it is not up to me to approve
Nice that you extracted chunk to ferrum

[route]

Nice work! Let me take a thorough look and I get back to you

[route]

I think it might be possible to check it even without switching frames, but not 100%

[myabc]

I tried removing just this frame switching but it broke the implementation - the original implementation of isObscured calls document.elementFromPoint(px, py) (always on the current window) and doesn't know how to traverse nested frames.

I've gone ahead and reimplemented the nested frame handling in JavaScript - Although I think it'd probably be a bit more concise to use recursion, I've used iteration as that's what's been used elsewhere (e.g. _frameOffset).

[route]

Awesome thanks!