[ios][precompile] add support for clang virtual file system

[chrfalch]

Summary:

To solve our problem with header files from the React.XCFramework not being consumable due to the legacy Cocoapods headers, we used to point all header search / resolving into the Pods/Headers folder when building even with the framework installed.

This is a problem since an xcframework expects a modular header structure that can be consumed from within the headers folder of the framework.

The headers are used for both Objective-c compiling and for creating clang modules that can be consumed by Swift in our setup.

This commit fixes the above issues and makes a modular clang virtual file system from the header files we distribute. This vfs-overlay file will then be used by the rncore.rb script when installing the 'React-Core-prebuilt' pod and map the header files requested in the source code to the actual location on disk where the React.xcframework headers are installed.

Here are the changes:

• Added vfs.js with types for creating clang virtual file system overlays
• Added resolving the paths in the vfs file to the actual install path
• Added installing the vfs overlay with the switch -ivfsoverlay <path> to compiler settings for both obj-c and swift on pod installation
• Add vfs targets to the app target on post install

Prev PR: https://github.com/facebook/react-native/pull/54841

Changelog:

[IOS] [FIXED] - added support for clang virtual file system in React.XCFramework

Test Plan:

Run RNTester with prebuilt

[github-actions[bot]]

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	:x:

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Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	:x:

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Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	:x: