Add support for `i` parameter in Press This

[stephdau]

I was browsing the Codex page for Press This (​https://codex.wordpress.org/Press_This#Technical_Note), and I noticed that there was a documented data param that wasn't replicated in the new version: i, to pass an image URL.

The attached patch enables that parameter (GET and POST), and offers the image to the user for selection (no auto-embed).

[Michael Arestad]

Is this necessary?

[stephdau]

It's definitely something that can be leveraged by 3rd-parties to integrate with PT at a basic level, and supposedly was there.

[kraftbj]

Chatter about this feature and to include it or not: ​https://wordpress.slack.com/archives/core-pressthis/p1430255033001395

[azaozz]

Perhaps we can add the extra image src at the bottom in merge_or_fetch_data(), prepending it to the existing array so it is shown as first choice. Seems a bit simpler, see 32173.2.diff.

[obenland]

It should be $_REQUEST['i'] rather than $_REQUEST('i').

Let's get this moving quickly, beta is only two weeks away.

[azaozz]

Replying to obenland:

Thanks for testing/catching the typo :) Fixed in 32173.3.diff.

[azaozz]

In 32936:

Press This: support passing i parameter to add an image src.
Props stephdau, azaozz. Fixes #32173.