fix: Change aria-label depending on content of paragraph block

[tofumatt]

Fix issue introduced in #11560.

This only shows an aria-label for RichText blocks when they aren't empty. I think it's a start; let me know if that fixes the issue I introduced in #11560
#11560 (comment).

[afercia]

Thanks @tofumatt
This actually renders an aria-label="false" where false is evaluated as a string and used as the attribute value.

Additionally, quoting from #1659:

The aria-label attribute works as a <label> element and gives a name to its control. So both when the Editable is empty or already filled up with content, screen readers will announce the Editable with the name given by the aria-label.

[sorry for my broken English]

the aria-label should identify what the Editable is. For a paragraph, it should say: Paragraph content or similar wording

The placeholder values:

are more "suggestions" that should go in a description (see #5981 (comment)). Instead, each editable field should be labelled to communicate what it is, as one would normally do for form fields.

[jasmussen]

I added a followup comment on the phrasing in #11560 (comment) — if that phrasing was intentional, then I won't be the blocker. But if it was a typo or slightly unintentional, do you think you could lump in the phrasing change in this PR? Thanks Matt.

[youknowriad]

I added to 4.3 as it's smallish we can get it quickly in.

[tofumatt]

I've updated the code to reflect the real state of this block; when empty it's functionally an empty block that by default accepts text to become a paragraph or the slash key to open the inserter.

Now the label instructs users what is there; when there is content: the label "Paragraph Block" is read. When there is no content: "Empty block; start writing or type forward slash to choose a block" is read.

I think that's a good solution for now.

I also tweaked the text as per @jasmussen's request.

[jasmussen]

Approving based on content of placeholder. Thanks so much for this, it's way better, and should pair nicely with #11659 which makes the text not wrap on mobile or in columns.

[mcsf]

You may want to wait for a second (Joen beat me to it!) 👍, but this looks correct to me.