FR: Add valueOf() to Timestamp instances #2632

[REQUIRED] Describe your environment

• Operating System version: macOS 10.15.2 (19C57)
• Browser version: Node v1.21.1
• Firebase SDK version: 7.13.0
• Firebase Product: Firestore

[REQUIRED] Describe the problem

Unable to compare Timestamp instances with native comparators. Javascript calls valueOf() on the object and uses the results of that to do native comparisons.

Steps to reproduce:

Attempt to compare Timestamps directly.

Relevant Code:

firebase = require('firebase-admin')
a = new firebase.firestore.Timestamp(1, 1)
b = new firebase.firestore.Timestamp(2, 2)
console.log(a < b) // false
console.log(b < a) // false

Workaround

Of course you can simply call toMillis() and compare those, but having it auto handled would be better.