Onboarding: Import button should be disabled if there's no selection

[bsclifton]

Description

If you install Brave and go through the steps in the onboarding, one is import. If you de-select everything, you can still click the Import button (although it doesn't do anything).

We should disable the button unless something is selected

Steps to Reproduce

1. Have other browsers installed (and have profile data for them)
2. Fresh install of Brave
3. Go through onboarding until Import screen
4. Deselect any browser selection (nothing should be selected)

Actual result:

Import button is active and clickable. Doesn't do anything - but it's not disabled.

Expected result:

Button should be disabled

[MadhaviSeelam]

Reproduced using STR #28788 (comment)

Brave | 1.49.132 Chromium: 111.0.5563.147 (Official Build) (64-bit)
-- | --
Revision | 029fd65a4dd711d1078468ed2206999cec86066b-refs/branch-heads/5563@{#1239}
OS | Windows 11 Version 22H2 (Build 22621.1413)

[kjozwiak]

The above requires 1.50.112 or higher for 1.50.x verification 👍

[GeetaSarvadnya]

Verification PASSED on

Brave | 1.50.113 Chromium: 112.0.5615.49 (Official Build) (64-bit)
-- | --
Revision | bd2a7bcb881c11e8cfe3078709382934e3916914-refs/branch-heads/5615@{#936}
OS | Windows 10 Version 21H2 (Build 19044.2728)

• Reproduced the issue on 1.50.108 and 1.50.110
  

Using the STR/Cases outlined via #28788 (comment), encountered the issue #29501 in step 4 (unable to Deselect any browser selection).

I have followed the following workaround to test the issue.

1. Set brave as default browser via windows->settings-Default apps
2. Uninstall the brave
3. make sure no browsers are set as default via windows->settings-Default apps
4. Install brave, navigate to Import settings screen
5. no browsers are selected on the Import settings screen

• ensured that Import is not clickable when a browser has not been selected during the Import phase
• ensured that selecting a browser enables the Import button without any issues
  • ensured that clicking the Import button works as expected and moves onto the next phase of Import

Example	Example