Add default browser shortcut to Custom Tabs dev setting

[joshliebe]

Task/Issue URL: https://app.asana.com/0/488551667048375/1207482546194311/f

Description

Adds a default browser shortcut to easily change the default browser when testing Custom Tabs.

Steps to test this PR

• [x] Go to Developer Settings > Custom Tabs
• [x] Tap “Default Browser"
• [x] Choose a default browser
• [x] Go back to the Custom Tabs dev screen
• [x] Verify that the selected browser’s name is displayed

UI changes

Before	After

[joshliebe]

• #4610 👈
• develop

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