isFeatureEnabled now returns true if multivariant flag

[marandaneto]

💡 Motivation and Context

By doing #41 I noticed that isFeatureEnabled is also wrong.

I also noticed that the iOS SDK never returns false if a flag has a false value.
https://github.com/PostHog/posthog-ios/blob/9298825fe26899a58b976d400254e0b050daa578/PostHog/Classes/PHGPostHog.m#L317
Is it a bug on the iOS SDK I believe, right?

💚 How did you test it?

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

[marandaneto]

Actually, I am a bit confused, the decide API does not return the disabled feature flags.

By disabled I mean this:

so if the flag is within the response payload, it is enabled, always, then the iOS implementation is correct.

Should isFeatureEnabled return false if the flag is within the payload but its value is false? on iOS this is never the case, it will always return true.
The older version of the Android SDK does what this PR is aiming to do.

@neilkakkar mind explaining?

[neilkakkar]

Decide returns all enabled flags, correct.

But just because a flag is enabled doesn't mean that the API will always return true. For example, if you have a filter on Country = X on the flag, the API will return false if you're outside country X.

Same for, say, if the rollout % is not 100%.

[neilkakkar]

Should isFeatureEnabled return false if the flag is within the payload but its value is false?

Correct, and nice finding!

[marandaneto]

To avoid pinterest/ktlint#1874