Mobile: Add a copy button in code block view

[mattermod]

Add a copy button on the full screen that shows the code of the mobile app.

Here’s a Figma file showing the same.

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Original issue reported:

https://github.com/mattermost/mattermost-mobile/issues/7659

Summary

Cannot copy text from a rendered code block.

Environment Information

• Mattermost App Version: 2.9.0 (Build 48903) and later versions
• Mattermost Server Version: 9.0.0 and later versions

Steps to reproduce

1. Send a formatted message like this.

   ```nim
   echo "Hello World"
   

2. Open the message & this code block.
3. You cannot copy its text.

Expected behavior

I can copy the code from the code screen with a copy button on the top right.

Observed behavior

Cannot copy the code from the code full screen. It can be copied by long pressing on the code block in the message.

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JIRA: https://mattermost.atlassian.net/browse/MM-56802

[apshada]

@amyblais Can i Work on this issue