Notification when attempting to import seed phrase in the wrong area on MM

**What problem are you trying to solve?**
Sometimes users try to import their seed phrase in the "import account" section.

**Describe the solution you'd like**
If someone starts to type in their seed phrase, a red notification should display as soon as the space bar is pressed, which would suggest a seed phrase and not a private key.

Start by locating the MetaMask extension's "import account" section and its private-key input. Reproduce entering a space-separated seed phrase and confirm where validation or notifications are handled; done means a red notification appears when the space bar indicates a seed phrase is being entered.

Written by the indexing model from the issue text.