What?

This PR truncates all block labels/titles returned from the BlockTitle hook, where a maximumLength prop is passed.

The consequence is that all block titles will be truncated, including core block title metadata.

We're also adding unit tests that test the priority of block labels.

Finally, I've updated the documentation to recommend against longer block titles as advised in #39110 (comment)

Why?

Previously only contextual block labels such as reusable block labels or block variation were truncated.

@gziolo rightly posed the question:

What if the block title has 100 characters? 😄
Maybe we should also truncate it for consistency when someone explicitly passes this parameter.

#39110 (comment)

How?

Calling truncate() where a maximumLength is passed.

Testing Instructions

Block titles appearing in the Editor Breadcrumb (at the bottom), Block settings Dropdowns, List view labels and Block Toolbar labels should appear as expected.

• In the editor, create a reusable block, preferably with a long name such as A really really really long name that doesn't really mean much but might be truncated if it all some time if we happen to care
• Insert a Row block (which is a Group block variation)
• Insert a regular Group block
• Check that the contextual labels (reusable, block variation) take priority over the core title (e.g., Group)
• Check that the truncation still works for very long titles
• Smoke test block titles in another local. I tried Arabic, Russian and German.