Customizer: Don't trigger a change event if two unchanged object values are equal.

In JavaScript: `{"title":"Foo"} !== {"title":"Foo"}`
Underscore.js provides an isEqual function to compare two values to see if they have the same contents, which can be use instead.
Because only one function of Underscore.js is needed we just add a copy of `_.isEqual` to customize-base.js.

props westonruter.
fixes #26061.
Built from https://develop.svn.wordpress.org/trunk@26548


git-svn-id: http://core.svn.wordpress.org/trunk@26440 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Heartbeat:
- Bring back heartbeat.interval().
- Rename wp_disable_heartbeat_suspend() to wp_heartbeat_set_suspension().
- Rename the option for disabling suspension from options.suspend to options.suspension.
Fixes #25073.
Built from https://develop.svn.wordpress.org/trunk@26549


git-svn-id: http://core.svn.wordpress.org/trunk@26441 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Comments moderation screen:
- Don't resize the textarea when replying to long comments.
- Limit the resizing of the textarea when quick-editing long comments to 500px.
Props SergeyBiryukov, fixes #25746.
Built from https://develop.svn.wordpress.org/trunk@26550


git-svn-id: http://core.svn.wordpress.org/trunk@26442 1a063a9b-81f0-0310-95a4-ce76da25c4cd