Add `Object` methods for handling nested objects

[Jongsun Suh]

The Object module currently lacks the following methods for accessing and updating nested properties.

• Object.AtPathN
  • Get the nested values in object O at the paths and keys specified in P.
  • (P: (PropertyKey | PropertyKey[])[], O: Record) --> ?
• Object.Update
  • Update a nested value in object O at path P.
  • (P: PropertyKey[], V: ?, O: Record) --> Record
• Object.UpdateN
  • Update multiple nested values in object O at paths and keys specified in P, using values specified in V.
  • (P: (PropertyKey | PropertyKey[])[], V: ?[], O: Record) --> Record

The implementation should include unit tests and JSDoc comments that adhere to the guidelines established in the style-guide/ directory.

[Jongsun Suh]

Closed by #82