fix(types): correct references to Buffer for @types/node >= 16.0.0 < 16.6.0

Fix #11963

Author: vkarpov15

types/inferschematype.d.ts

@@ -142,7 +142,7 @@ type ResolvePathType<PathValueType, Options extends SchemaTypeOptions<PathValueT
     PathValueType extends StringConstructor | 'string' | 'String' | typeof Schema.Types.String ? PathEnumOrString<Options['enum']> :
       PathValueType extends NumberConstructor | 'number' | 'Number' | typeof Schema.Types.Number ? number :
         PathValueType extends DateConstructor | 'date' | 'Date' | typeof Schema.Types.Date ? Date :
-          PathValueType extends BufferConstructor | 'buffer' | 'Buffer' | typeof Schema.Types.Buffer ? Buffer :
+          PathValueType extends typeof Buffer | 'buffer' | 'Buffer' | typeof Schema.Types.Buffer ? Buffer :
             PathValueType extends BooleanConstructor | 'boolean' | 'Boolean' | typeof Schema.Types.Boolean ? boolean :
               PathValueType extends 'objectId' | 'ObjectId' | typeof Schema.Types.ObjectId ? Schema.Types.ObjectId :
                 PathValueType extends 'decimal128' | 'Decimal128' | typeof Schema.Types.Decimal128 ? Schema.Types.Decimal128 :

types/types.d.ts

@@ -2,6 +2,8 @@
 declare module 'mongoose' {
   import mongodb = require('mongodb');
 
+  class NativeBuffer extends Buffer {}
+
   namespace Types {
     class Array<T> extends global.Array<T> {
       /** Pops the array atomically at most one time per document `save()`. */
@@ -47,7 +49,7 @@ declare module 'mongoose' {
       unshift(...args: any[]): number;
     }
 
-    class Buffer extends global.Buffer {
+    class Buffer extends NativeBuffer {
       /** Sets the subtype option and marks the buffer modified. */
       subtype(subtype: 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 128 | ToObjectOptions): void;