Use API Availability Checks instead of PF_UNAVAILABLE_WARNING

[JohnCaccavale]

• [x] I am not disclosing a vulnerability.
• [x] I am not just asking a question.
• [x] I have searched through existing issues.
• [x] I can reproduce the issue with the latest versions of Parse Server and the Parse ObjC SDK.

Issue Description

Some classes and API are unavailable for all platforms. In some cases, to indicate a particular class is unavailable, various macros are used such as PF_OSX_UNAVAILABLE_WARNING, PF_TV_UNAVAILABLE_WARNING, PF_WATCH_UNAVAILABLE_WARNING, etc.

This unfortunately results in unnecessary warnings in the Xcode Issue Navigator even if a client project makes no use of those API.

Rather than generating these warnings, these macros should be removed in favor of @available API checks.

Steps to reproduce

• Create a macOS project and add the latest Parse SDK as a dependency via Swift Package Manager.
• Upon building the macOS project, the warnings appear in the issue navigator.

Actual Outcome

• Warnings appear in the issue navigator that need not to occur.

Expected Outcome

• If not utilizing unavailable API, there should be no project warnings.

Environment

• ParseObjc Version 3.0.0
• Xcode Version 15.3 (15E204a)

Client

• Parse ObjC SDK version: 3.0.0

[parse-github-assistant[bot]]

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