feat: fieldlabel change pulled from rsp@v3

[jianliao]

Description

Mainly change was pulled from this PR 298

How and where has this been tested?

• How this was tested:
• Browser(s) and OS(s) this was tested with:

Screenshots

To-do list

• [x] If my change impacts other components, I have tested to make sure they don't break.
• [x] If my change impacts documentation, I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.

• [ ] This pull request is ready to merge.

[adobe-spectrum-bot]

Test result: http://opensource.adobe.com/spectrum-css-vr-results/999d5c7-result-2020-05-18_15-48-22/html_report/

Dev Site: http://opensource.adobe.com/spectrum-css-vr-results/999d5c7-result-2020-05-18_15-48-22/dist/docs/

[adobe-spectrum-bot]

Test result: http://opensource.adobe.com/spectrum-css-vr-results/169e155-result-2020-05-18_18-07-23/html_report/

Dev Site: http://opensource.adobe.com/spectrum-css-vr-results/169e155-result-2020-05-18_18-07-23/dist/docs/

[jianliao]

Hi @GarthDB @lazd, This PR combined all the change pulled from RSP@v3 for fieldlabel, fieldgroup and form components. There are quite a few breaking changes like css class name changes and dom markup changes. I've tried my best to fix all CSS example YAML files, which match the latest RSP@v3, to uncover these changes to you.

Please review it carefully and I'll leave it you to discuss with RSP team if their naming changes does not comply with our naming convention.

[adobe-spectrum-bot]

VRT successfully! :confetti_ball:

View the VRT result

[pfulton]

Closing due to the many changes involved with the migration to the new tokens system. We can reopen or integrate the code from this PR in the future if we need to.