fix: ensure the default ID of the first player is 'vjs_video_3' as some people have relied on this

[misteroneill]

Description

When a player is created without an id on the embed code, Video.js automatically assigns it one based on an auto-incrementing number (a.k.a. a GUID). For the longest time, this has happened to result in the default id of the first player being vjs_video_3.

It was never intended for users to rely on this value being consistent, but users do strange and inadvisable things.

PR #6103 had an unintended side effect in that it changed the default id to vjs_video_2, which we worry could affect some users of Video.js.

Specific Changes proposed

• Increment the internal starting point of the GUID from 1 to 3.
• Avoid doing anything that increments the GUID simply by including Video.js on the page.
• Add a test that simulates the initial player creation by resetting the GUID to its initial value to verify that the first player created has its id assigned as vjs_video_3.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[misteroneill]

This should probably be merged to a branch off of 7.6.4 as that's what I based this branch on.

[brandonocasey]

Code looks good, and from a test with data-setup and a player with no id this looks good. I wonder if we should have a sandbox page for data-setup so this can more easily be tested in the future

[misteroneill]

Maybe, but data-setup wasn't involved here. The changes to setup.js are there to prevent the incrementing of the GUID before any players are created.

[brandonocasey]

data-setup is just an easy way to force videojs to use a guid for a element with no id attribute.

[gkatsev]

Tested locally, works fine for manually created and data-setup cases.