Update the embed block to show no preview for smugmug embeds

[brentswisher]

Description

Fixes #11960 by adding smugmug.com to the array of domains that the "no-preview" screen is shown. Also adjusted the matching criteria to grab the base domain instead of just stripping "www." off of the host if found. This was necessary as smugmug embeds are in the format "username.smugmug.com"

How has this been tested?

Manually tested to verify that both individual photos and galleries display the no preview message using:
https://johndavis.smugmug.com/Nature/Landscape/i-NntLPZ8
https://johndavis.smugmug.com/Nature/Landscape

Screenshots

Types of changes

New feature (non-breaking change which adds functionality)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[notnownikki]

looks good to me 🚢

[jasmussen]

❣️

[paaljoachim]

I am doing some general testing on GB version 5.0 RC-1.
I am reacting to the word sorry.

"Sorry, this embedded content cannot be previewed in the editor."
---> It feels a lot better with "Embedded content cannot be previewed in the editor."
Or "Smugmug embedded content cannot be previewed in the editor."

[jasmussen]

@paaljoachim Good point. Feel free to create a new ticket, you can ping me if you'd like it categorized well. I imagine such a change would be ripe territory for "Good First Ticket" labels.

[aduth]

It's very non-obvious to me as a future maintainer what it is we're trying to accomplish here with this logic. It would have been very helpful to include one or more of an inline code comment, separate named and documented function, and unit test.