Re-export config-plugins from expo package and update docs

[brentvatne]

Why

jakobo/expo-community-flipper#16

Fixes ENG-6059

Checklist

• Documentation is up to date to reflect these changes (eg: https://docs.expo.dev and README.md).
• Conforms with the Documentation Writing Style Guide.

[linear]

ENG-6059 Explain for third party library authors how to add a config plugin dependency to a library

• peer dependency on expo
• peerdependenciesmeta to mark as optional

[amandeepmittal]

LGTM 👍

[brentvatne]

The following packages currently use private APIs from @expo/config-plugins, so I didn't change them to use the new format yet:

• expo-build-properties: @expo/config-plugins/build/utils/generateCode, @expo/config-plugins/build/plugins/android-plugins (for mocking in test), @expo/config-plugins/build/plugins/ios-plugins (for mocking in test)
• expo-camera: @expo/config-plugins/build/utils/generateCode
• expo-image-picker: @expo/config-plugins/build/android/Manifest
• expo-dev-client: @expo/config-plugins/build/android/Manifest

I think we should fix these in a follow-up PR. @EvanBacon - should we be exposing Manifest and generateCode through the public API?

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[KiwiKilian]

@rnmapbox/maps also uses some private APIs which are currently not exported with the new style:

import {
  mergeContents,
  removeGeneratedContents,
} from '@expo/config-plugins/build/utils/generateCode';

Do you already have any followup issue on this topic?

[brentvatne]

@KiwiKilian - you should be able to copy and paste those functions out into the mapbox library, these aren't intended to be public APIs. ideally we want to come up with a better API for interacting with podfile

[SimenB]

Official plugins also use it. https://github.com/expo/config-plugins/blob/ed020d236b8fa4a810adf90a9773d9a2fba36fd4/packages/react-native-pdf/src/withPdf.ts#L7

Maybe expose it as unstable or something up until a replacement is made?