Make it possible for Obj-C view controller to implement IndicatorInfoProvider protocol

[oduwa]

In order to display a View Controller (VC) as a child of a Pager controller, the child VC needs to conform to the IndicatorInfoProvider protocol in order to let the pager know what to use as the VC's title in the pager.

However, if a VC is written in Obj-C, it is currently impossible to have it as a child of a pager because the IndicatorInfoProvider protocol isn't made available to Obj-C. In order to make it available, the following minor changes have been made:

• Added the @objc flag to the protocol
• Structs don't exist in Obj-C, but the protocol function returns a struct. Refactored its return type to be a Class instead of a Struct.

[oduwa]

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