Add xAI model provider icon

[Giuspepe]

Summary

• update @vscode/codicons to 0.0.46-28 for the updated Moonshot AI glyph and new xAI glyph
• register the xAI codicon and use it for Grok/xAI models, including BYOK models
• avoid applying Copilot branding to unknown third-party models solely because they are hosted by the Copilot provider
• add model provider icon coverage for Copilot-hosted Grok, agent-host Grok, BYOK xAI, and generic DeepSeek models

Fixes https://github.com/microsoft/vscode-internalbacklog/issues/8658
Depends on microsoft/vscode-codicons#506.

Validation

• npm run compile
• ./scripts/test.sh --grep ModelProviderIcons — 2 passing
• launch-skill verification with the published codicons package:
  • selected live Grok 4.5 and verified chat-model-provider-xai renders U+ECEC
  • selected live Kimi K3 and verified the updated chat-model-provider-kimi glyph renders

[Copilot]

Pull request overview

Adds xAI branding for Grok models and updates the bundled Codicons dependency.

Changes:

• Registers the new xAI codicon.
• Assigns provider icons for Grok/xAI and generic third-party models.
• Expands model-provider icon tests.

Show a summary per file

File	Description
modelProviderIcons.test.ts	Adds provider-icon coverage.
modelProviderIcons.ts	Adds xAI icon selection and refines Copilot branding.
codiconsLibrary.ts	Registers the xAI glyph.
remote/web/package.json	Updates the remote-web Codicons dependency.
remote/web/package-lock.json	Locks the updated remote-web dependency.
package.json	Updates the root Codicons dependency.
package-lock.json	Locks the updated root dependency.

Review details

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• remote/web/package-lock.json: Generated file

• Files reviewed: 5/7 changed files
• Comments generated: 1
• Review effort level: Balanced