Local state of objects not correct if setting multiple properties

[mortenmo]

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest versions of Parse Server and the Parse JS SDK.

Issue Description

When looking at #1798 found that setting multiple properties on the same object locally without saving reports the wrong object back. It will only show (this is true for set and unset) the latest Op you added to that property and not all. So setting data.b and data.c without saving (or you're offline), causes data.b to not be set.

When the object gets saved, the properties show up on get as expected.

Steps to reproduce

const myObj = new Parse.Object('MyClass');
myObj.set('data', {a: 5});
await myObj.save(null, {useMasterKey: true});

myObj.set('data.b', 2);
myObj.set('data.c', 2);

console.log(myObj.get('data'));

Actual Outcome

{ a: 5, c: 2}

Expected Outcome

{ a: 5, b: 2, c: 2}

Environment

Server

• Parse Server version: 7.0.0
• Operating system: OSX
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): Local

Client

• Parse JS SDK version: 5.0.0

[parse-github-assistant]

Thanks for opening this issue!

• 🚀 You can help us to fix this issue faster by opening a pull request with a failing test. See our Contribution Guide for how to make a pull request, or read our New Contributor's Guide if this is your first time contributing.

[dplewis]

Completed via #1451