[Paywalls V2] Allowing intro eligibility overrides for text (and image and stack)

[joshdholtz]

Motivation

Need to show different text when intro offer is eligible

Description

New IntroEligibilityContext object that will store the eligibility cache for the paywall components to reference

• Reused TrialOrIntroEligibilityChecker from Paywalls V1
• Stored as a StateObject on the paywall parent
• Passed as an environment object to children components
• Eligibility is fetched on load (async) and will be propagated to children components
  • All eligibility should already be cached in the SDK so it should be fairly instant

[joshdholtz]

@JayShortway I added your comments into https://github.com/RevenueCat/purchases-ios/pull/4495/commits/e00f6a7621e02eb3f7b8eabac6ae09e5f16c2125 💪

I also merged the restructure PR into this before doing so 🤦‍♂️