Provides a meaningful error message for the dependency conflict occuring when there is no stable version available for a given pod and user do not specify pod version explicitly in Podfile.

While handling resolver error in `handle_resolver_error` method of `resolver.rb` file, we will check if the specificati
on that is not satisfying given requirement was a pre-release version, and if the requirement was including any explicit version or source. If spec is a pre-release version, and there is no explicit version or source for the requirement, we will print a message directing the user to specify pre-release version explicitly.

Remove SDKROOT relative search path

This was causing warnings with the iOS 9 SDK as this path doesn't even
exist anymore and seemingly wasn't needed since XCTest came along.

Fixes #4168

[Sandbox::FileAccessor] Add C++ Sources (.i)

[Validator] build watchOS pods against watchossimulator for validation 🌈

This reverts commit c521ad1e.

Added the cocoapods-search plugin to CocoaPods

[Resolver] Allow platform detection to work for nested dependencies

[FileAccessor] Take exclude_files into account for resource_bundles

[Analyzer] Dont create cycles when computing transitive dependencies

[PodTargetInstaller] Mark all headers with availability levels