Summary:
Pull Request resolved: https://github.com/facebook/flipper/pull/3139
This commit adds new UI in the top level toolbar to allow internal FB users to switch between the internal build of devtools and the OSS one.
## Scenarios
**Internal (when `client.isFB`)**
- DevTools version will default to the internal version, and will render a `Select` component with option to switch to the OSS version.
- If a global install of DevTools is present, the selection menu will also offer the option to switch to the global DevTools version.
**External (when `!client.isFB`)**
Will preserve previous behavior:
- Uses the OSS version by default, and doesn't provide option to switch to internal version.
- If a global installation is present, will render a `Switch` component that allows switching between OSS and global installation.
### Implementation
This commit refactors some parts of the DevTools plugin to provide a bit more clarity in the loading sequence by renaming and modifying some of the messaging, and fixing lint warnings.
A change introduced here is that when switching or loading devtools, when we attempt to reload the device via Metro, don't immediately show a "Retry" button, since at that point nothing has gone wrong, and the Retry button will only occur if the Metro reload doesn't occur after a few seconds.
In a future commit, this [PR in Devtools](https://github.com/facebook/react/pull/22848) will allow us to clear any loading messages once DevTools has successfully connected.
Reviewed By: lunaruan, mweststrate
Differential Revision: D32773200
fbshipit-source-id: aa15ffecba7b2b2ea74e109e9f16334d47bf5868
