[a11y] Add high contrast highlight to common suggestion box
[a11y] Add high contrast highlight to common suggestion box

This change adds CSS rules to show the selected suggested box item
when in forced-color mode (high contrast).

The suggestion box is used for autocomplete in the elements style panel
and the console input (and all other codemirror inputs).

Note that to test this change you must first enabled chrome://flags#forced-colors.

I consider this change low-risk after looking at usages of suggestion
box, the biggest is the text prompt [1].

This will fix other areas of the devtools and allow us to start
removing redundant styling for forced-colors [2].

[1]: https://source.chromium.org/search?q=TextPrompt%20-f:out%20-f:test%20f:.js&ss=chromium&originalUrl=https:%2F%2Fcs.chromium.org%2F
[2]: https://source.chromium.org/search?q=forced-color-adjust%20-f:out%20-f:test%20f:.css%20path:devtools-frontend&ss=chromium&originalUrl=https:%2F%2Fcs.chromium.org%2F

Screenshot (styles pane): https://imgur.com/wL4uriI
Screenshot (console): https://imgur.com/t6zub3n

Change-Id: Ifcf3270c0d7c91e2aad79037d8a5de2c7bbc8ce6
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2212431
Reviewed-by: Robert Paveza <7787129de3d0cb4911c68d958db3023863584560@microsoft.com>
Reviewed-by: Kalon Hinds <0953a07de5dd99912b5643571c8ed9864c017a6d@microsoft.com>
Commit-Queue: John Emau <c153e6e600be23fb28cec0b08551440e4bf7575d@microsoft.com>

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