fix warning from using deprecated TSC URL (#4110)

motivation: TSC URL is deprecated

changes:
* migrate the url scheme parsing code to the one call site that needs it

Sources/PackageLoading/ManifestJSONParser.swift

@@ -13,10 +13,6 @@ import Foundation
 import PackageModel
 import TSCBasic
 
-import struct TSCUtility.URL
-
-fileprivate typealias URL = Foundation.URL
-
 enum ManifestJSONParser {
     private static let filePrefix = "file://"
 
@@ -250,7 +246,7 @@ enum ManifestJSONParser {
               )
             }
             return AbsolutePath(location).pathString
-        } else if TSCUtility.URL.scheme(dependencyLocation) == nil {
+        } else if parseScheme(dependencyLocation) == nil {
             // If the dependency URL is not remote, try to "fix" it.
             // If the URL has no scheme, we treat it as a path (either absolute or relative to the base URL).
             return AbsolutePath(dependencyLocation, relativeTo: packagePath).pathString
@@ -415,6 +411,33 @@ enum ManifestJSONParser {
         )
     }
 
+    /// Parses the URL type of a git repository
+    /// e.g. https://github.com/apple/swift returns "https"
+    /// e.g. git@github.com:apple/swift returns "git"
+    ///
+    /// This is *not* a generic URI scheme parser!
+    private static func parseScheme(_ location: String) -> String? {
+        func prefixOfSplitBy(_ delimiter: String) -> String? {
+            let (head, tail) = location.spm_split(around: delimiter)
+            if tail == nil {
+                //not found
+                return nil
+            } else {
+                //found, return head
+                //lowercase the "scheme", as specified by the URI RFC (just in case)
+                return head.lowercased()
+            }
+        }
+
+        for delim in ["://", "@"] {
+            if let found = prefixOfSplitBy(delim), !found.contains("/") {
+                return found
+            }
+        }
+
+        return nil
+    }
+
     /// Looks for Xcode-style build setting macros "$()".
     private static let invalidValueRegex = try! RegEx(pattern: #"(\$\(.*?\))"#)
 }