Update the summarization button when summarization is happening

[dkotter]

What?

Closes #381

Updates the summarization buttons to say Generating... when summarizations are being generated.

Why?

While we have a loading state on these buttons, updating the text makes it more clear and matches how we do things in other experiments.

How?

Updates both the button in the post status sidebar and the button that shows in the AI Summarization block toolbar to show Generating... when generation is in progress

Use of AI Tools

None

Testing Instructions

1. Pull this branch down and run npm i && npm run build
2. Add a valid AI Connector
3. Turn on the Summarization experiment
4. Create a post
5. Find the Generate Summary button in the post status sidebar and click it
6. Ensure the text updates to say Generating...
7. Once the AI Summary block has been inserted, click into that block and ensure the generate icon shows in the block toolbar
8. Click this and hover over it, ensuring the tooltip shows Generating...

Screenshots or screencast

summarization.mov

[github-actions]

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Co-authored-by: dkotter <dkotter@git.wordpress.org>
Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.81%. Comparing base (aa6409b) to head (aac4353).

Additional details and impacted files

@@            Coverage Diff             @@
##             develop     #382   +/-   ##
==========================================
  Coverage      63.81%   63.81%           
  Complexity       684      684           
==========================================
  Files             49       49           
  Lines           3529     3529           
==========================================
  Hits            2252     2252           
  Misses          1277     1277           

Flag	Coverage Δ
unit	63.81% <ø> (ø)

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