Add support for dropdown container to be inline-block (#8559)

[jffng]

Description

This change adds a prop to the Dropdown component that allows a user to set the containing element to display inline-block. This allows the popover to appear centered relative to its trigger in instances outside of the Gutenberg context.

How has this been tested?

Tested in the Gutenberg playground and passes respective unit tests.

Screenshots

Before

After

Types of changes

Fixes #8559

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[youknowriad]

While triaging the repository I found this PR. Sorry for the delay here, we should have taken a look earlier.

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Why did you decide on a prop here? Should this be the default behavior of the Dropdown instead?

[jffng]

Hello!

Why did you decide on a prop here?

I used a prop as a convenience, giving the consumer of the component a method to handle an expected use case (display the popover aligned to the button), while not changing the default behavior.

Should this be the default behavior of the Dropdown instead?

I'm not sure - I would need to look more thoroughly throughout the repo to see where and how the Dropdown component is used, and what effects the change would have.

[youknowriad]

So I went ahead and included this change in #18631 in addition to other dropdown changes. Thanks a lot for your contribution