Support icon variant on commands, make start and stop icons filled

[JamesNK]

Description

Consistent feedback on the start/stop/restart icons was the stop icon looked like an empty checkbox. The standard for this kind of UI is to have filled icons. For example, VS debugging start/stop buttons are filled.

This PR:

• Adds icon variant option to commands. Defaults to regular.
• Changes start and stop icons to be filled icons.
• Changes the icon size from 20 to 16. Size 20 filled icons felt too big. Size 16 looks good.
• Fixes error when command doesn't have an icon.

Demo:

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue:
  • No

Microsoft Reviewers: Open in CodeFlow

[drewnoakes]

Looks much better.

[JamesNK]

/azp run

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[JamesNK]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).