Improve inline doc descriptions in `media-views.js`.

Props ericlewis.
See #28459.

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git-svn-id: http://core.svn.wordpress.org/trunk@28506 1a063a9b-81f0-0310-95a4-ce76da25c4cd
As per @gcorne's suggestion, when calling `wp.mce.views.register()`, automatically set `shortcode` equal to the passed `type` in the set of default args instead of introducing a `type` property. It is still overrideable by the args that are passed.

See #28458.


Built from https://develop.svn.wordpress.org/trunk@28689


git-svn-id: http://core.svn.wordpress.org/trunk@28507 1a063a9b-81f0-0310-95a4-ce76da25c4cd