reflect: fix Value.NumMethod docs

NumMethod counts unexported methods for interface types. This
behavior is documented in Type.NumMethod

Fixes #42123

Change-Id: Ia5aba353a8cc64190c701d1521972d57e8903564
Reviewed-on: https://go-review.googlesource.com/c/go/+/396075
Reviewed-by: Ian Lance Taylor <[email protected]>
Trust: Cherry Mui <[email protected]>

Author: zlasd

src/reflect/type.go

@@ -72,7 +72,9 @@ type Type interface {
 
 	// NumMethod returns the number of methods accessible using Method.
 	//
-	// Note that NumMethod counts unexported methods only for interface types.
+	// For a non-interface type, it returns the number of exported methods.
+	//
+	// For an interface type, it returns the number of exported and unexported methods.
 	NumMethod() int
 
 	// Name returns the type's name within its package for a defined type.

src/reflect/value.go

@@ -1868,7 +1868,11 @@ func (v Value) Method(i int) Value {
 	return Value{v.typ, v.ptr, fl}
 }
 
-// NumMethod returns the number of exported methods in the value's method set.
+// NumMethod returns the number of methods in the value's method set.
+//
+// For a non-interface type, it returns the number of exported methods.
+//
+// For an interface type, it returns the number of exported and unexported methods.
 func (v Value) NumMethod() int {
 	if v.typ == nil {
 		panic(&ValueError{"reflect.Value.NumMethod", Invalid})