[xcodegen] Fix hasPrefix for paths

The intention here was to do a component-wise
prefix check, not sure why I did a string prefix
check. Switch to component prefix and rename to
`starts(with:)` to match `FilePath`.

Author: hamishknight

utils/swift-xcodegen/Sources/SwiftXcodeGen/BuildArgs/SwiftTargets.swift

@@ -285,7 +285,7 @@ struct SwiftTargets {
 
   func getTargets(below path: RelativePath) -> [SwiftTarget] {
     targets.filter { target in
-      guard let parent = target.buildRule?.parentPath, parent.hasPrefix(path) 
+      guard let parent = target.buildRule?.parentPath, parent.starts(with: path) 
       else {
         return false
       }

utils/swift-xcodegen/Sources/SwiftXcodeGen/Generator/ProjectGenerator.swift

@@ -154,8 +154,9 @@ fileprivate final class ProjectGenerator {
     guard let path else { return true }
 
     // Not very efficient, but excludedPaths should be small in practice.
-    guard let excluded = spec.excludedPaths.first(where: { path.hasPrefix($0.path) })
-    else {
+    guard let excluded = spec.excludedPaths.first(
+      where: { path.starts(with: $0.path) }
+    ) else {
       return true
     }
     if let description, let reason = excluded.reason {
@@ -238,7 +239,9 @@ fileprivate final class ProjectGenerator {
               group(for: repoRelativePath.appending(parentPath)) != nil else {
         // If this isn't a child of an explicitly added reference, something
         // has probably gone wrong.
-        if !spec.referencesToAdd.contains(where: { parentPath.hasPrefix($0.path) }) {
+        if !spec.referencesToAdd.contains(
+          where: { parentPath.starts(with: $0.path) }
+        ) {
           log.warning("""
             Target '\(name)' at '\(repoRelativePath.appending(parentPath))' is \
             nested in a folder reference; skipping. This is likely an xcodegen bug.

utils/swift-xcodegen/Sources/SwiftXcodeGen/Path/PathProtocol.swift

@@ -78,8 +78,8 @@ public extension PathProtocol {
     return exts.contains(where: { ext == $0.rawValue })
   }
 
-  func hasPrefix(_ other: Self) -> Bool {
-    rawPath.hasPrefix(other.rawPath)
+  func starts(with other: Self) -> Bool {
+    self.storage.starts(with: other.storage)
   }
 
   var components: FilePath.ComponentView {