[WIP] Block Editor: Add contextual label for block inserter button

[shrivastavanolo]

What?

Closes #71162

This PR updates the block inserter button label to show a contextual and clearer message when adding new blocks inside a parent block. Instead of the generic "Add block" tooltip, it shows "Add block to [Parent Block Title]" where applicable (e.g., for navigation menu items).

Why?

The generic "Add block" tooltip can be confusing when adding items inside blocks like the Navigation block, where users expect to add a new menu item rather than just a generic block. This change improves clarity by specifying the type of item being added based on the parent block's title.

How?

• The ButtonBlockAppender component now receives a parentBlockTitle prop and uses it to customize the button label.
• The label changes from a generic "Add block" to a contextual string, e.g., "Add block to Navigation" for navigation blocks.
• The Inserter component obtains the parent block title by retrieving the parent block's block type title or name and passes it down as a prop.
• The label text uses WordPress translation functions (_x and sprintf) with translator comments for internationalization support.

Reference taken from here: #45238 (comment)

Testing Instructions

1. Open the editor and add a Navigation block (or any block with nested child blocks).
2. Hover over or focus the block inserter button inside the parent block.
3. Confirm that the tooltip/button label reads "Add block to [Parent Block Title]" (e.g., "Add block to Navigation") instead of the generic "Add block."
4. Verify that the label is properly translated and appears correctly for other block types as well.

Screencast

Before

Screen.Recording.2025-08-11.at.12.22.50.PM.mov

After

Screen.Recording.2025-08-11.at.12.57.01.PM.mov

[getdave]

Thanks for this PR.

I was looking at the same problem in #71502. I think there's some overlap here and it's possible both approaches can co-exist.

I think there are some situations where we might want to change this label to not be about blocks at all.

For example, in the Navigation block, the concept of "block" is less applicable. We want the appender to read Add page because the "Page link" variation is the default block for the Nav block. I wonder how this can be achieved.

I also note that the addition of the block title/name here increases the verbosity of the tooltip. However, I see that accessibility feedback has noted this would be an enhancement in that regard. We should probably request some design feedback here as well so that we can strike a balance that works for all users.

I also see that once I add a Group the appender + that appears still reads Add block

[github-actions]

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