Improve docs for WP_Dependencies/WP_Styles/WP_Scripts and related functions

[ocean90]

Tickets which introduced mentioned classes/function:

• #2701 – Centralize javascript inclusions
• #3911 – Javascript should not be localized by via PHP
• #7011 – Create wp_print_styles() to match wp_print_scripts()
• #8628 – Extend class WP_Scripts to support concatenating, compressing and printing scripts in the HTML head and the footer

[ocean90]

In 36729:

Docs: Use correct @since tags for script enqueue functions.

See [4968], [3788].
See #35964.

[ocean90]

In 36730:

Docs: Document properties of WP_Scripts and add missing @since tags.

See #35964.

[ocean90]

In 36731:

Docs: In WP_Dependencies add a changelog entry to methods which were moved from WP_Scripts to WP_Dependencies.

See #35964.

[ocean90]

In 36732:

Docs: In WP_Dependencies add a changelog entry for the $group parameter.

See #35964.

[ocean90]

In 36733:

Docs: Add missing @since tags to WP_Styles properties/methods.

See #35964.

[ocean90]

@DrewAPicture I'd like to get rid of the references to BackPress in the file headers and class docs. Any objections to this?

[DrewAPicture]

@ocean90 Nope. I talked to @johnjamesjacoby about this a couple of months ago and the consensus was: go ahead.

[ocean90]

In 36744:

Docs: Improve inline docs for WP_Dependencies, WP_Styles, and WP_Scripts.

Also, make them and related files part of WordPress.

See #35964.