feat: Add Target.validatedSources to filter the sources that are invalid (#153)

* Expose an API to return the validated sources

* Mark supportsSources as deprecated

Author: pepicrft

Sources/XcodeGraph/Models/Target.swift

@@ -204,6 +204,11 @@ public struct Target: Equatable, Hashable, Comparable, Codable, Sendable {
         }
     }
 
+    @available(*, deprecated, message: """
+    Whether a target supports sources or not is not as binary decision as we originally assumed and codified in this getter.
+    Because it's something that depends on other variables, we decided to pull this logic out of tuist/XcodeGraph into tuist/tuist.
+    If you are interested in having a similar logic in your XcodeGraph-dependent project, you might want to check out tuist/tuist.
+    """)
     /// Returns true if the target supports having sources.
     public var supportsSources: Bool {
         switch product {