[7.x] Set APPLICATION_EXTENSION_API_ONLY to YES

[ikesyo]

This enables us to use Swift internal classes from Objective-C side with importing the generated header.

Fixes #477.

[wongzigii]

Should we also turn on APPLICATION_EXTENSION_API_ONLY in Quick ?

[ikesyo]

Might be yes: Quick/Quick#749

[wongzigii]

[ghost]

This is causing a warning in my project:

Any fixes for that?

[axandreo]

I am getting the same warning as @afetrifork . Additionally, I can't tell if they're related but, I started getting this issue

Analyzing dependencies
[!] Unable to satisfy the following requirements:

- `Nimble` required by `Podfile`
- `Nimble` required by `Podfile`
- `Nimble (= 7.1.2)` required by `Podfile.lock`

None of your spec sources contain a spec satisfying the dependencies: `Nimble, Nimble (= 7.1.2)`.

The error instructs me to do pod repo update. However, invoking pod repo update doesn't solve this error.