Change access control for DatadogInternal API

[marksands]

Feature description

I'm getting a symbol name collision with a function that's defined in DatadogInternal https://github.com/DataDog/dd-sdk-ios/blob/ca533286e991d4c05096ccbfb6a5309b254036ee/DatadogInternal/Sources/Utils/SwiftExtensions.swift#L118

Since a lot of the API in that module is public, it's being imported through my client code as well. Swift 5.9 added a new access control level called package SE-386, so the other SPM libraries can use that code without it leaking into the client. The only way I'm able to solve my issue is renaming my subscript extension, which is a bit unfair.

Proposed solution

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Other relevant information

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