External Libraries: First step of updating jQuery. Disable jQuery Migrate...

External Libraries: First step of updating jQuery. Disable jQuery Migrate 1.4.1, keep jQuery at 1.12.4-wp, and UI at 1.11.4. Also keep the `jquery-core` script handle for full backwards compatibility.

Props jorbin, adamsilverstein, westonruter, retlehs, pento, onokazu, galbaras, netweb, zakkath, dmethvin, LittleBigThing, markgoho, iandunn, remzicavdar, bigcloudmedia, jacklinkers, levdbas, a4jpcom, azaozz.

See #37110.
Built from https://develop.svn.wordpress.org/trunk@48323


git-svn-id: https://core.svn.wordpress.org/trunk@48092 1a063a9b-81f0-0310-95a4-ce76da25c4cd