Implement stub for NavigatorPlugins

[jdm]

Servo has no support for traditional browser plugins, so the actual implementation should be fairly straightforward (ie. returning None/0/false, etc.).

Spec: https://html.spec.whatwg.org/multipage/webappapis.html#plugins-2 (and add Navigator implements NavigatorPlugins;)
Code:

• in components/script/dom/webidls/:
  • Navigator.webidl, PluginArray.webidl, Plugin.webidl, MimeTypeArray.webidl, MimeType.webidl
• in components/script/dom/:
  • navigator.rs, pluginarray.rs, plugin.rs, mimetypearray.rs, mimetype.rs
    Tests:
• ./mach test-wpt tests/wpt/mozilla/tests/mozilla/interfaces.html (modify this test to pass)
• ./mach test-wpt tests/wpt/web-platform-tests/html/dom/interfaces.html (update the interfaces.html.ini file to accommodate the new passing tests)

See the documentation for steps to follow when adding new WebIDL interfaces.

This work is important because when navigator.plugins is missing, clicking links on Twitter is broken (see #9870).

[jdm]

Claiming this temporarily for potential RGSoC applicants. Please contact me before starting to work on this.

[jdm]

This is available for anyone to work on.

[cbrewster]

I would like to work on this one.

[jdm]

Go ahead!

[cbrewster]

Implemented in #10485