fix(type): add IAlwaysOnTopAPI interface and update references

[dipanshurdev]

📝 Description

This PR addresses several TypeScript issues related to the Always-on-Top feature. It introduces a formal interface for the alwaysOnTop API and fixes a type error where window.alwaysOnTop was reported as non-existent by IDEs despite being documented in globals.d.ts.

🚀 Key Improvements

• Strong Typing: Introduced IAlwaysOnTopAPI in react/features/always-on-top/types.ts.
• Refined Declarations: Improved Window interface augmentation in globals.d.ts to use the new interface and marked alwaysOnTop as optional for improved runtime safety across different app windows.
• Improved DX: Resolved the "Property 'alwaysOnTop' does not exist" error commonly seen in IDEs (VS Code).
• Bug Fix: Fixed setSinkId signature in globals.d.ts to return Promise<void> instead of Promise<undefined>.

✅ Verification Results

• npm run tsc:web: Passed (verified 0 errors in Always-on-Top components)
• npm run lint:ci: Passed

🧪 Testing Performed

• Verified that all calls to api methods in VideoMuteButton, AudioMuteButton, Toolbar, and AlwaysOnTop components now have correct IntelliSense and type checking.

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.