[SourceControl] Add default implementation for some new methods

Author: aciidgh

Sources/SourceControl/Repository.swift

@@ -99,6 +99,12 @@ public protocol RepositoryProvider {
     func openCheckout(at path: AbsolutePath) throws -> WorkingCheckout
 }
 
+extension RepositoryProvider {
+    public func checkoutExists(at path: AbsolutePath) throws -> Bool {
+        fatalError("Unimplemented")
+    }
+}
+
 /// Abstract repository operations.
 ///
 /// This interface provides access to an abstracted representation of a
@@ -201,6 +207,12 @@ public protocol WorkingCheckout {
     func areIgnored(_ paths: [AbsolutePath]) throws -> [Bool]
 }
 
+extension WorkingCheckout {
+    public func areIgnored(_ paths: [AbsolutePath]) throws -> [Bool] {
+        fatalError("Unimplemented")
+    }
+}
+
 /// A single repository revision.
 public struct Revision: Hashable {
     /// A precise identifier for a single repository revision, in a repository-specified manner.