Represent browsers as Browser objects internally

[flotwig]

Current behavior:

Inside the launcher package, browser is treated as an object with a name, a version, a path to the browser...

packages/launcher/lib/types.ts

Inside the server package, the browser is treated as an object (at first), but is quickly reduced to just the name (chrome, chromium, ...)

This means there's not much flexibility in how we can detect different browsers and then pass that information to the rest of Cypress.

Desired behavior:

Modify the internal representation of browsers from just the name to always be the full Browser object, to enable new functionality like selecting browser by version (#3183), using arbitrary paths to browsers (#1026), and using proper display names in the desktop-gui.

[cypress-bot]

Released in 3.2.0.