1883157 - Add 'create profile' behavior to submenu

Status: NEW

(Toolkit :: Startup and Profile System, enhancement)

Description

[Jared Hirsch [:jhirsch] (he/him) (Needinfo please)]

Following on bug 1883155, here we need to make the "Create a new profile" menu item do the right thing when clicked.

First, we need to create and launch a new profile, which should be code that's in about:profiles somewhere. (Call into gProfiles when clicked to handle the click.)

Second, interestingly, we need to force the new profile to launch with about:profiles-new displayed (so that they can customize their new profile). This will require some investigation to figure out. There's also a bunch of weird homepage override code in BrowserContentHandler to look through; we need to override the overrides somehow.

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References:

Eng doc: https://docs.google.com/document/d/1R2462LEfagLI1y37hO90zlcKnGgQbhZvLG3lGtWEN84/edit?usp=sharing

Product MVP doc: https://docs.google.com/document/d/1am6FmSPBi0zTtGQZbINEUjDsvgD2BuS8ho-ERUB624w/edit

Very WIP Figma link: https://www.figma.com/file/FXL6eQGaZ3MI50XebsCIJ8/Profiles?type=design&node-id=5203-5997&mode=design&t=CtvoRiYXfBmkZhDd-0