Update cell hover styles

[julieg18]

2/2 main <- #2197 <- this

• add cell horizontal borders instead of updating cell background color, fixing invisible (or near invisible) checkboxes in some themes.

Example of main cell hover style:

Example of PR cell hover style:

https://user-images.githubusercontent.com/43496356/184978628-df891c38-c2a1-46be-8f0a-890302709822.mov

Part of #2133 followup

[shcheklein]

I don't like tbh, how text is moving a few pixels as you hover. Is it a bug or a feature?

[shcheklein]

Color also doesn't change - is it expected?

[julieg18]

I don't like tbh, how text is moving a few pixels as you hover. Is it a bug or a feature?

Whoops, wrong video! Text shouldn't be moving now.

Color also doesn't change - is it expected?

Yes, we originally wanted to add a background color to the cells, but I'm having trouble finding a background color that works well across themes 🤔

Another option I considered was having the cell hover background be the table color, with or without borders:

[qlty-cloud-legacy[bot]]

Code Climate has analyzed commit 9066afca and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (85% is the threshold).

This pull request will bring the total coverage in the repository to 96.6% (0.0% change).

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