Add focus ring for <SelectableCardSolid>

[filiptronicek]

Description

Adds focus rings to the cards component for improved accessibility.

Related Issue(s)

Split from #17053

Partly addresses #16723

How to test

Go to the preview environment, to user preferences, and Tab your way through to the Theme selection. It should always be clear which one is selected.

Documentation

Preview status

Gitpod was successfully deployed to your preview environment.

• 🏷️ Name - ft-selecta9ef3ce70f0
• 🔗 URL - ft-selecta9ef3ce70f0.preview.gitpod-dev.com/workspaces.
• 📚 Documentation - See our internal documentation for information on how to interact with your preview environment.

Build Options:

• /werft with-werft
  Run the build with werft instead of GHA
• leeway-no-cache
• /werft no-test
  Run Leeway with --dont-test

Publish Options

• /werft publish-to-npm
• /werft publish-to-jb-marketplace

Installer Options

• analytics=segment
• with-dedicated-emulation
• with-ws-manager-mk2
• workspace-feature-flags
  Add desired feature flags to the end of the line above, space separated

Preview Environment Options:

• /werft with-local-preview
  If enabled this will build install/preview
• /werft with-preview
• /werft with-large-vm
• /werft with-gce-vm
  If enabled this will create the environment on GCE infra
• with-integration-tests=all
  Valid options are all, workspace, webapp, ide, jetbrains, vscode, ssh

/hold

[filiptronicek]