[ML] Migrate SCSS to emotion for data grid

[walterra]

Summary

Part of #140695.

Migrate SCSS to emotion for data grid mini histograms.

Checklist

• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: e269ba7

Failed CI Steps

• FTR Configs #49

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
ml	1728	1718	-10

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
ml	3.4MB	3.4MB	-2.0KB

Unknown metric groups

ESLint disabled line counts

id	before	after	diff
securitySolution	394	397	+3

Total ESLint disabled count

id	before	after	diff
securitySolution	474	477	+3

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @walterra

[mdefazio]

LGTM

[peteharverson]

Tested and LGTM.

Not related to the changes here, but I noticed that the color contrast on mouse hover for the histogram bars is much less noticeable in light theme:

than in dark mode:

The styling for dark mode is better for accessibility. Wonder if the light mode theme could be tweaked easily as part of this PR?

[walterra]

@peteharverson Added a note about revisiting the colors/contrast regarding accessibility to the data grid histograms meta issue: #71231