Update mediaelement.js to fix Vimeo auto play issues.

[danieliser]

WP core currently includes mediaelementjs v4.2.6.

Due to recent browser changes Vimeo videos no longer will auto play and often get errors.

A patch was made for this by adding allow="autoplay; fullscreen" here 12 days ago: ​https://github.com/mediaelement/mediaelement/issues/2618

I propose either:

• Updating this dependency to the latest master branch which is currently [6 commits](​https://github.com/mediaelement/mediaelement/compare/4.2.9...master) ahead of the latest available release.
• Updating this dependency to the [latest release](​https://github.com/mediaelement/mediaelement/releases) (v4.2.9) & manually patching the [6 commits](​https://github.com/mediaelement/mediaelement/compare/4.2.9...master) as needed.
• Manually patching the existing version included with WP core to include this and a few other improvements based on changes to modern browsers over the past year.

Master is stable from what I can tell, but as its not versioned and I'm not sure if core would directly accept it without its official release.

This is the specific patch that fixes the Vimeo issue: ​https://github.com/mediaelement/mediaelement/commit/e84fa56ced5653408203dd0f0db76a05af497720

Personally since core is on 4.2.6 I see no reason we can't feasibly update to the current master branch and mark it as 4.2.9 so that in the future updates will work fine.

[danieliser]

Patched with latest master branch build of mediaelement.js vendor libraries.

[danieliser]

Updated the script-loader.php version for mediaelement vendor library to 4.2.9-a6cc75b (refernce to latest commit hash).

[danieliser]

@adamsilverstein - Any word when this will be included? Still getting regular complaints.

[Hareesh Pillai]

Updates mediaelement.js from v4.2.6 v4.2.12

[Hareesh Pillai]

Patch 46681.diff updates mediaelement.js from v4.2.6 to v4.2.12

All the QUnit test cases are passing after this update.

This update includes many bug fixes and a minor accessibility improvement.
Changelog: ​https://github.com/mediaelement/mediaelement/blob/master/changelog.md

[adamsilverstein]

In 46681.2.diff​:

• Latest version from ​https://github.com/mediaelement/mediaelement/releases/tag/4.2.13.

Test running: ​https://travis-ci.com/WordPress/wordpress-develop/builds/130980868

[adamsilverstein]

add commit hash since 4.2.13 is unreleased

[adamsilverstein]

In 46436:

External Libraries: upgrade mediaelement to version 4.2.13.

Upgrade mediaelement to the latest version. Includes a variety of bug fixes made since the 4.2.6 release; see ​https://github.com/mediaelement/mediaelement/releases.

Props danieliser, Hareesh Pillai.
Fixes #46681.