Add confirmation dialog when inviting users with unknown identities

[kaylendog]

Content

Introduces a new confirmation modal that appears when a user attempts to invite users who's cryptographpic identities have not been cached.

Part of element-hq/element-meta#3163

Motivation and context

It might be quite easy to accidentally typo a user ID, and invite a user that we haven't previously interacted with. When this happens, we won't have a record of their identity, so it might be an easy attack for the server to replace their identity with an attacker-controlled identity.

While the initial motivation behind these changes was to prevent sending historic room keys to members we might not mean to, there are more general arguments to be made.

Screenshots / GIFs

Tests

TODO

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• This PR was made with the help of AI:
  • Yes. In this case, please request a review by Copilot.
  • No.
• Changes have been tested on an Android device or Android emulator with API 24
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request title will be used in the release note, it clearly defines what will change for the user
• Pull request includes screenshots or videos if containing UI changes
• You've made a self review of your PR

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Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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