Disable save button when no detail present

[darkdh]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

fix #4855

Auditors: @bbondy

Test Plan:

1. Open "about:autofill"
2. Click "Add Address"
3. The save button should be disabled
4. Enter the detail of form, the save button should be enabled
5. Remove all detail of form, the save button should be disabled
6. Open "about:autofill"
7. Click "Add Credit Card"
8. The save button should be disabled
9. Enter the detail of form, the save button should be enabled (Name, Card Number)
10. Remove all detail of form, the save button should be disabled (Name, Card Number)
11. Open "about:autofill"
12. Add address entry
13. Edit the address entry
14. Remove all detail of form, the save button should be disabled
15. Open "about:autofill"
16. Add credit card entry
17. Edit the credit card entry
18. Remove all detail of form, the save button should be disabled (Name, Card Number)

[bbondy]

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