Ensure 0x-prefixed addresses in send input

[FrederikBolding]

Explanation

Ensures hex-prefixed addresses in send input.

More Information

TBD

Manual Testing Steps

1. Paste a non 0x prefixed address in the send input
2. Try to send a token to that address
3. See that this works

Pre-Merge Checklist

• PR template is filled out
• IF this PR fixes a bug, a test that would have caught the bug has been added
• PR is linked to the appropriate GitHub issue
• PR has been added to the appropriate release Milestone

+ If there are functional changes:

• Manual testing complete & passed
• "Extension QA Board" label has been applied

[danjm]

closing in favour of #15064