[Firestore] Resolve protocol conformance warnings (#13484)

Author: ncooke3

Firestore/Swift/Source/Codable/DocumentReference+Codable.swift

@@ -50,4 +50,4 @@ extension CodableDocumentReference {
   }
 }
 
-extension DocumentReference: CodableDocumentReference {}
+extension FirebaseFirestore.DocumentReference: FirebaseFirestore.CodableDocumentReference {}

Firestore/Swift/Source/Codable/FieldValue+Encodable.swift

@@ -21,7 +21,7 @@
 #endif // SWIFT_PACKAGE
 
 /** Extends FieldValue to conform to Encodable. */
-extension FieldValue: Encodable {
+extension FirebaseFirestore.FieldValue: Swift.Encodable {
   /// Encoding a FieldValue will throw by default unless the encoder implementation
   /// explicitly handles it, which is what Firestore.Encoder does.
   public func encode(to encoder: Encoder) throws {

Firestore/Swift/Source/Codable/GeoPoint+Codable.swift

@@ -63,4 +63,4 @@ extension CodableGeoPoint {
 }
 
 /** Extends GeoPoint to conform to Codable. */
-extension GeoPoint: CodableGeoPoint {}
+extension FirebaseFirestore.GeoPoint: FirebaseFirestore.CodableGeoPoint {}

Firestore/Swift/Source/Codable/Timestamp+Codable.swift

@@ -59,4 +59,4 @@ extension CodableTimestamp {
 }
 
 /** Extends Timestamp to conform to Codable. */
-extension Timestamp: CodableTimestamp {}
+extension FirebaseCore.Timestamp: FirebaseFirestore.CodableTimestamp {}

Firestore/Swift/Source/Codable/VectorValue+Codable.swift

@@ -58,4 +58,4 @@ extension CodableVectorValue {
 }
 
 /** Extends VectorValue to conform to Codable. */
-extension VectorValue: CodableVectorValue {}
+extension FirebaseFirestore.VectorValue: FirebaseFirestore.CodableVectorValue {}