Introduce Patches: changes to be uploaded to the server

[jingtang10]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Description
Introduce the concept of Patch, which is the changes to be sent to the server. More specifically:

• Introduce Patch class, which is very similar to the LocalChange class at the moment
• Change the result of "squashing" to Patches
• Chagne the input of request generation to Patches
• Remove the UploadWorkManager function getPendingUploadsIndicator and inline its implementation, paving the way for removing UploadWorkManager altogether

Remaining issues:

• The local change tokens are created by simply concatenating the tokens from all local changes. This only works now for upload bundle sizes less than 500. If the bundle size is greater than 500, local change tokens will be missed. This needs to be addressed in a follow up PR.

Alternative(s) considered
Have you considered any alternatives? And if so, why have you chosen the approach in this PR?

Type
Feature

Screenshots (if applicable)

Checklist

• I have read and acknowledged the Code of conduct.
• I have read the Contributing page.
• I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA.
• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach.
• I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project.
• I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally.
• I have built and run the demo app(s) to verify my change fixes the issue and/or does not break the demo app(s).

[anchita-g]

LGTM

[omarismail94]

This change is so good!

[omarismail94]

GREAT change! just some uber nits