fix: update Foundation.swift for cocoa pods

[TheRogue76]

Bit of a doozy, but basically, when it comes to SPM, the GRMustacheKeyAccess is a package that you import, but when it comes to Cocoapods, this is already bundled next to it and is NOT a separate package, so when you call import, it will fail, which means you can't build when using cocoa pods.

This PR adds a check to see if that even exists before trying to import it, addressing the issue for both SPM and Cocoapods (tried both locally but feel free to try as well)

[TheRogue76]

@fumito-ito can you check this as well?

[fumito-ito]

@TheRogue76 Thanks for your PR. However, I encountered an error when running pod lib lint --allow-warnings on my macOS. The error message is as follows:

NOTE  | [iOS] xcodebuild:  clang: error: SDK does not contain 'libarclite' at the path '/Applications/Xcode-16.0.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/arc/libarclite_iphonesimulator.a'; try increasing the minimum deployment target

It seems similar to this issue: CocoaPods/CocoaPods#11839.

[TheRogue76]

@fumito-ito Interesting. I will try to find some time this weekend / tomorrow and try seeing what is going on and report back. Seems like a removed dependency on newer tool chains.

[TheRogue76]

Ok @fumito-ito It appears that the matter is due to Xcode deprecating the older targets libarclite. As mentioned by Apple here Bumping the target to iOS 11 is now a requirement for using cocoa pods with the require_arc. I am bumping it on the pod file as well in this PR just to be in sync. Let me know your thoughts and if you want me to bump the SPM one as well. I also bumped the Swift Version to 5.9 because Xcode 15 is the oldest version that can actually send builds to App Store Connect now, and all older versions are defunct

[fumito-ito]

Thanks @TheRogue76 . I believe raising the target is a reasonable change. I will update the SPM target, but I will create a separate PR for that myself.