reflect/protoregistry: remove Files.Find{Enum,Message,Extension,Service}ByName

This is a breaking change.

The replacement is the Files.FindDescriptorByName method,
which is more flexible as it handles all descriptor types.

Change-Id: I2ccd544a7630396a2428b1d41f836c5246070912
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/183700
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/filedesc/build.go b/internal/filedesc/build.go
index 28bd370..5f46e34 100644
--- a/internal/filedesc/build.go
+++ b/internal/filedesc/build.go
@@ -40,8 +40,7 @@
 	// If nil, it uses protoregistry.GlobalFiles.
 	FileRegistry interface {
 		FindFileByPath(string) (protoreflect.FileDescriptor, error)
-		FindEnumByName(pref.FullName) (pref.EnumDescriptor, error)
-		FindMessageByName(pref.FullName) (pref.MessageDescriptor, error)
+		FindDescriptorByName(pref.FullName) (pref.Descriptor, error)
 		Register(...pref.FileDescriptor) error
 	}
 }
diff --git a/internal/filedesc/desc_lazy.go b/internal/filedesc/desc_lazy.go
index 3583012..9fc5b1b 100644
--- a/internal/filedesc/desc_lazy.go
+++ b/internal/filedesc/desc_lazy.go
@@ -33,8 +33,8 @@
 			// Weak fields are only resolved by name.
 			if fd.L1.IsWeak {
 				r := file.builder.FileRegistry
-				if md, _ := r.FindMessageByName(fd.L1.Message.FullName()); md != nil {
-					fd.L1.Message = md
+				if d, _ := r.FindDescriptorByName(fd.L1.Message.FullName()); d != nil {
+					fd.L1.Message = d.(pref.MessageDescriptor)
 				}
 				continue
 			}
@@ -106,8 +106,8 @@
 			return ed2
 		}
 	}
-	if ed2, _ := r.FindEnumByName(ed.FullName()); ed2 != nil {
-		return ed2
+	if d, _ := r.FindDescriptorByName(ed.FullName()); d != nil {
+		return d.(pref.EnumDescriptor)
 	}
 	return ed
 }
@@ -124,8 +124,8 @@
 			return md2
 		}
 	}
-	if md2, _ := r.FindMessageByName(md.FullName()); md2 != nil {
-		return md2
+	if d, _ := r.FindDescriptorByName(md.FullName()); d != nil {
+		return d.(pref.MessageDescriptor)
 	}
 	return md
 }
diff --git a/internal/filetype/build.go b/internal/filetype/build.go
index 635099b..fa1bb9a 100644
--- a/internal/filetype/build.go
+++ b/internal/filetype/build.go
@@ -274,8 +274,7 @@
 	}
 	fileRegistry interface {
 		FindFileByPath(string) (pref.FileDescriptor, error)
-		FindEnumByName(pref.FullName) (pref.EnumDescriptor, error)
-		FindMessageByName(pref.FullName) (pref.MessageDescriptor, error)
+		FindDescriptorByName(pref.FullName) (pref.Descriptor, error)
 		Register(...pref.FileDescriptor) error
 	}
 )