Fix duplicate password reveal icon

[Copilot]

Description

Secret text fields in the unresolved parameters dialog could briefly show two reveal icons in Microsoft Edge: the browser-provided password reveal control and Aspire's custom accessible reveal button. The dialog now suppresses Edge's native control inside the Fluent text field's shadow DOM before rendering Aspire's button, so exactly one reveal affordance is visible.

The suppression is idempotent, applies to every secret field, and is retried when dialog content is re-rendered. Component coverage verifies that the native control is suppressed before one custom button is rendered, and browser coverage verifies that the suppression style is installed inside the Fluent component's shadow root.

User-facing usage

When an unresolved parameter uses the secret text input type, the dashboard displays one reveal button beside the masked value instead of briefly displaying two.

Screenshots / Recordings

This PR includes UI changes. Please add screenshots or screen recordings so reviewers can evaluate the visual changes without running locally.

• For before/after comparisons, place them side-by-side or label them clearly.
• For interactive changes (animations, transitions, new flows), prefer a short screen recording (GIF or video).
• If you cannot capture visuals now, note what scenario to test and mark this section as TODO.

TODO: Capture the unresolved parameters dialog with a pre-populated secret value in Microsoft Edge. Before this change, the native and Aspire reveal icons briefly overlap; after this change, only Aspire's reveal button is shown.

Validation: JavaScript syntax and focused helper behavior pass locally. The targeted dashboard component test could not run because the configured dnceng Arcade SDK feed returned HTTP 403 while restoring Microsoft.DotNet.Arcade.Sdk.

Fixes # (issue)

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

Created from a Microsoft Teams conversation.