fix(index.d.ts): improve context and type bindings for `Schema#method…

…s` and `Schema#statics`

Fix #9717

index.d.ts

@@ -1086,11 +1086,11 @@ declare module 'mongoose' {
 
     /** Adds an instance method to documents constructed from Models compiled from this schema. */
     // eslint-disable-next-line @typescript-eslint/ban-types
-    method(name: string, fn: Function, opts?: any): this;
-    method(obj: { [name: string]: Function }): this;
+    method(name: string, fn: (this: DocType, ...args: any[]) => any, opts?: any): this;
+    method(obj: { [name: string]: (this: DocType, ...args: any[]) => any }): this;
 
     /** Object of currently defined methods on this schema. */
-    methods: { [name: string]: (this: DocType, ...args: any[]) => void };
+    methods: { [F in keyof DocType]: DocType[F] } & { [name: string]: (this: DocType, ...args: any[]) => any };
 
     /** The original object passed to the schema constructor */
     obj: any;
@@ -1144,12 +1144,12 @@ declare module 'mongoose' {
 
     /** Adds static "class" methods to Models compiled from this schema. */
     // eslint-disable-next-line @typescript-eslint/ban-types
-    static(name: string, fn: Function): this;
+    static(name: string, fn: (this: M, ...args: any[]) => any): this;
     // eslint-disable-next-line @typescript-eslint/ban-types
-    static(obj: { [name: string]: Function }): this;
+    static(obj: { [name: string]: (this: M, ...args: any[]) => any }): this;
 
     /** Object of currently defined statics on this schema. */
-    statics: { [name: string]: Function };
+    statics: { [F in keyof M]: M[F] } & { [name: string]: (this: M, ...args: any[]) => any };
 
     /** Creates a virtual type with the given name. */
     virtual(name: string, options?: any): VirtualType;