[Emotion] Convert EuiHealth

[cee-chen]

Summary

Converts EuiHealth to CSS-in-JS and also removes the extra CSS text size modifier classes - I grepped through Kibana and confirmed that no tests are using said classes as hooks; only storybook snapshots will need to be updated.

Things to look out for when moving styles

- [ ] Anything in the backlog that could be a quick fix for that component?
- [ ] Convert global Sass vars to JS version like sizing
- [ ] Convert side specific padding, margin, and position to -inline and -block (Logical properties)
- [ ] Reduce specificity where possible (usually by reducing class name chaining)
- [ ] Use gap property to add margin between items if using flex
- [ ] Can any still existing .js files be converted to TS?

• Convert component-specific Sass vars to exported JS versions

QA

• Does the output CSS match the previous CSS / as expected
• Does the rendered class read as expected

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5832/

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5832/

[cee-chen]

@breehall Do you mind taking a look and reviewing this PR? Thanks a million! 🙏

[breehall]

This looks great! One thing I noticed was when comparing the PR Preview of the EUI docs to the current version of EUI, the line height seems to be a tad bit smaller.
It looks like the line-height in this PR is 1.4286rem, and in the current version of EUI it's 1.71429rem. This isn't a huge change, but I just wanted to bring it up just in case the change wasn't intended.

[cee-chen]

Ahh, thanks for catching this! I missed that the new euiFontSize() mixin sets line-height whereas the old Sass only sets font-size.

@cchaos, do you mind chiming in here? Is setting line-height alongside font-size the correct approach, or should I opt to use euiFontSizeFromScale() instead of euiFontSize()?

[cee-chen]

I'm just going to go ahead and change euiFontSize to euiFontSizeFromScale

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5832/

[cee-chen]

I totally misinterpreted what prod was doing with line-height. It looks like we should be keeping that in and using the new line height base determined by euiFontSize. I've reverted the commits around that

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5832/

[breehall]

Looks good to me! ✨