docs: update developer content

[zeroedin]

What I did

1. Updated content in the developer section

TODO:

• Fix testing screenshot images with the latest UI

Testing Instructions

1. View Deploy preview, review developer section of docs

Notes to Reviewers

1. Review modified content, and suggest changes.

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[zeroedin]

Note, reverting back to draft: forgot I still wanted to replace screenshots.

[zeroedin]

@bennypowers npm run test:ci fails when testing the whole project. Failures in react/vue tests I think are the majority of the issues although I didn't go through the failures 1 by 1. My assumption is that these passes/fails are dependent on react/vue wrapper conversation.

For now, I modified the testing section and only suggested testing the pf-cool-element which passes and allowed me to add the screenshot. npm run test:ci --files elements/**/pf-cool-element.spec.ts.

I think ideally long term the preference would be to get the whole project passing npm run test:ci and then revert that change back in docs to the global test run. Is this worthy of its own issue? Or is it close enough related to: #2370

[brianferry]

Do we use chai anymore in the app? No, right? If so we can remove that section from the 'testing' docs as well.

[bennypowers]

Do we use chai anymore in the app? No, right? If so we can remove that section from the 'testing' docs as well.

We do use chai. expect().to.whatever is chai