Add flow for no browser detected when onboarding

[rebron]

Description

If no browsers are detected during the onboarding v2 import flow, show the Choose your theme screen. Default to match system setting. When selecting dark mode, change background of buttons to reflect dark mode choice.

Steps to reproduce:

1. Fresh install of Brave on macOS with only Safari installed.
2. Notice screen in actual result.

Actual result:

Expected result:

https://www.figma.com/file/MFHpcXJMg2RUQpUJMAZZ4R/Desktop-Onboarding?node-id=3325%3A42022&t=LEYjscmyx6nVbe4p-0

Reproduces how often:

Easily.

Brave version (brave://version info)

1.47.x

Version/Channel Information:

• Can you reproduce this issue with the current release? n/a
• Can you reproduce this issue with the beta channel? yes
• Can you reproduce this issue with the nightly channel? yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? n/a
• Does the issue resolve itself when disabling Brave Rewards? n/a
• Is the issue reproducible on the latest version of Chrome? n/a

Miscellaneous Information:

[jenn-rhim]

How confident are we in detecting that there is no settings to import? Is there a possibility of false negative? If there is a possibility, we may need to accommodate that use case, and allow manual operation.
@rebron

[rebron]

@jenn-rhim Fairly confident. I tested on a normal user's machine and encountered this case.

[kjozwiak]

The above requires 1.47.154 or higher for 1.47.x verification 👍

[stephendonner]

Verified PASSED using

Brave	1.47.154 Chromium: 109.0.5414.46 (Official Build) beta (x86_64)
Revision	6e36b77363ef3febbe792af680fa1367993ddcf0-refs/branch-heads/5414@{#709}
OS	macOS Version 13.2 (a) (Build 22D7750270d)

Original issue:

Reproduced the original issue by following the below Prerequisites steps, using 1.47.151:

Prerequisites:

• removed all profile folders for various browsers, in /Users/sdonner/Library/Application\ Support/
• removed Opera's com.operasoftware.Opera file object in the above, top-level
• ran the Reset Safari Using Terminal section from https://www.makeuseof.com/reset-safari-default-mac/ line-by-line:

mv ~/Library/Safari ~/Desktop/Safari-`date +%Y%m%d%H%M%S`;
rm -Rf ~/Library/Cache/*;
rm -Rf ~/Library/Caches/Apple\ -\ Safari\ -\ Safari\ Extensions\ Gallery;
rm -Rf ~/Library/Caches/Metadata/Safari;
rm -Rf ~/Library/Caches/com.apple.Safari;
rm -Rf ~/Library/Caches/com.apple.WebKit.PluginProcess;
rm -Rf ~/Library/Cookies/*;
rm -Rf ~/Library/Cookies/Cookies.binarycookies;
rm -Rf ~/Library/Preferences/Apple\ -\ Safari\ -\ Safari\ Extensions\ Gallery;
rm -Rf ~/Library/Preferences/com.apple.Safari.LSSharedFileList.plist;
rm -Rf ~/Library/Preferences/com.apple.Safari.RSS.plist;
rm -Rf ~/Library/Preferences/com.apple.Safari.plist;
rm -Rf ~/Library/Preferences/com.apple.WebFoundation.plist;
rm -Rf ~/Library/Preferences/com.apple.WebKit.PluginHost.plist;
rm -Rf ~/Library/Preferences/com.apple.WebKit.PluginProcess.plist;
rm -Rf ~/Library/PubSub/Database;
rm -Rf ~/Library/Safari/*;
rm -Rf ~/Library/Safari/Bookmarks.plist;
rm -Rf ~/Library/Saved\ Application\ State/com.apple.Safari.savedState;

Case 1: Dynamic auto-mode selection with Match system setting selected - PASSED

Brave, Dark (Auto)	macOS, Dark	Brave, Light (Auto)	macOS, Light

Confirmed setting Match system setting dynamically follows the selected Light or Dark macOS theme setting

Case 2: Override the OS setting via Light mode and Dark mode - PASSED

Brave, Dark	macOS, Light	Brave, Light	macOS, Dark

Confirmed the Brave setting overrides the macOS system setting

Case 3: Skip, then Finish on Choose your theme defaults pref to same as macOS - PASSED

Brave Dark, Skip	macOS, Light	Brave Light, same as macOS

Confirmed Skipping the Choose your theme screen with Dark mode selected, on a Light macOS system defaults to Light, via the Brave Colors Same as macOS setting