Make all the 'Loading' strings consistent

[afercia]

Description

In the editor, while some parts of the UI are still loading their content, some text is used to inform users content is still loading. For example, the list of pages in the Site editor:

These strings are inconsistent:

• Some of the use an ellipsis at the end, some don't.
• One string has a trailing period.
• One string has an extraneous space.

Here's the strings in the current codebase that start with Loading:

Loading options…
Loading … (notice the space before the ellipsis)
Loading Navigation block setup options.
Loading pages
Loading patterns
Loading templates

Personally, I'd vote for always using the ellipsis, as that seems to be the most common pattern historically used in Core.
Extraneous spaces and period should be removed.
Waiting for design feedback… 🙂

Step-by-step reproduction instructions

• Scan the codebase for translatable strings that start with Loading. A good pattern for the search is: __( 'Loading
• See the inconsistencies in the strings.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes