[Login/Signup] 'Email' placeholder text is displaced after long string was removed

### Expected
If the Email field contains no text, the default `Email` placeholder text should be always fully visible.

### Observed
If the entered text was long enough to cause the 'extension' of input field length, the `Email` placeholder text will be outside the visible area, once the long text is deleted.

### Reproduced
1. Be logged out
2. Enter a long text into email field. Example: `quite_a_long_email_address@test.com`
3. Make sure the cursor is at the end of the string
4. Select all with `Cmd+A`
5. Delete ~> you will see the placeholder text being hidden (partly or completely depending on the previous string length)

https://user-images.githubusercontent.com/73365754/110338214-6e765880-802f-11eb-869a-562aaa919bab.mov

Make|Model|macOS Version|App Version
-|-|-|-
Mac|MBP 16|Big Sur 11.2|2.9 (11223)

Start by reproducing the problem in the macOS Login/Signup Email field using the listed long address and deletion steps. Find the Login/Signup UI entry point and verify the fix by confirming that deleting a long value leaves the full `Email` placeholder visible.

Written by the indexing model from the issue text.