feat: make getWorkspace, getFlyout, and getToolbox public

[NeilFraser]

Amusingly Flyout.isVisible and .setVisible are public, but there's no way to access a flyout given that getFlyout was not public.

[BeksOmega]

This LGTM but reassigned approval to Maribeth since this is a design decision. Also relevant forum link for context: https://groups.google.com/g/blockly/c/31Om9fkkAWA/m/fQuAg2-JBAAJ

[maribethb]

LGTM, but as Rachel said in the forum post, this is not just a documentation change, since we are formalizing these as part of the API. Even before TypeScript, these were marked @package so even though they have been used and recommended publicly they have never been actually declared as such.

So I would rename this PR: feat: make getWorkspace, getFlyout, and getToolbox public to make better release notes.

[cpcallen]

Because I really enjoy admiring Chesterton's Fence: do we know why these were originally @package and not @public? @rachel-fenichel?

[BeksOmega]

Because I really enjoy admiring Chesterton's Fence: do we know why these were originally @package and not @public? @rachel-fenichel?

I looked at the original PR (#771) and couldn't find a reason.

[rachel-fenichel]

Back then we didn't really talk about the flyout as a public API. There weren't any ways to customize it.