Ensure pattern categories always render in the Inserter

[scruffian]

What problem does this address?

Since #61108, there are several conditions under which the patterns tab doesn't display patterns:

1. There is no block selected
2. The theme removes support for core block patterns: remove_theme_support( 'core-block-patterns' );
3. The patterns haven't loaded yet.

In each of these cases we show this message in the patterns tab:

What is your proposed solution?

We should treat each of these situations differently:

1. We should still show the patterns and just insert them at the end of the content
2. We show a message to explain why
3. We show a loading placeholder

It would be useful to have designs for these states. cc @jasmussen @richtabor

[jasmussen]

This issue feels very reminiscent of #60991, enough that if we can do this:

We should still show the patterns and just insert them at the end of the content

It would likely solve both. We might refine this to "nearest insertable location" rather than "at the end". But wouldn't that mainly be the case? And if we can solve this, do we need loading placeholders or messages?

[jasmussen]

CC: @jameskoster

[richtabor]

We could combine these into one no results found view:

There's already a spinner used when pulling results from the block directory.; we could reuse that UX pattern:

As aside, but the Inserter should probably not render a "no results found" and a spinner at the same time.

[richtabor]

The theme removes support for core block patterns: remove_theme_support( 'core-block-patterns' );

I removed the needs design label. I think it's fine if the pattern inserter says "No results found" when there are no patterns.

Although if there are patterns insertable, you should see the pattern categories available. That we should resolve.

[jorgefilipecosta]

Although if there are patterns insertable, you should see the pattern categories available. That we should resolve.

It seems like this is already fixed. When there is no block selected, we can still use the inserter and see the pattern categories, the pattern is inserted at the end of the post.
The inserter already does not render a spinner and no results are found at the same time, if the patterns are loading only a spinner is rendered.

I'm going to close this issue, but I would appreciate if someone could double-check if I'm missing anything please feel free to reopen.