Yuhsuan/null check tsc silent

[YuHsuan-Hwang]

Description

This PR is for the first part of #2343. Files in /utilities, /models, and /services are migrated with the strictNullChecks option enabled.

A new script is added to trigger a separate ts compiler with the strcitNullChecks option enabled. tsc-silent is applied to suppress errors from files that are not migrated yet.

• To run the null checks, run npm run strict-null-checks. This is also triggered before development and production builds so that developers and the CI are aware of the checks.
• To include files for the null checks, add the files in the migratedFiles list in tsc-silent.config.js.

Checklist

For linked issues (if there are):

• assignee and label added
• ZenHub issue connection, board status, and estimate updated

For the pull request:

• reviewers and assignee added
• ZenHub estimate, milestone, and release (if needed) added
• changelog updated / no changelog update needed
• unit test added (for functions with no dependenies)
• API documentation added (for public variables and methods in stores)

For dependencies:

• e2e test passing / corresponding fix added / new e2e test created
• protobuf version bumped / no protobuf version bumped needed
• protobuf updated to the latest dev commit / no protobuf update needed
• corresponding ICD test fix added (BackendService changed) / no ICD test fix needed (BackendService unchanged)
• user manual prepared (for large new features)

[YuHsuan-Hwang]

Revised some fixes by changing the variable types instead of the values. Hope this reduces the possibility of regressions.

[YuHsuan-Hwang]

@crocka Thanks for reviewing the changes! Please check my replies and revision.

[kswang1029]

No regression from e2e tests. With some other manual tests based on the changed files in the codebase, so far I do not see odd behaviors. Certainly my manual test coverage is not complete, but let's just proceed and see if there are issues from the tests in the future.

[acdo2002]

The BackendService modification has been applied to the MessangeController.ts in the ICD-RxJS repository. (ICD-RxJS branch mylin/modify_MessageController_IBackendResponse)
The ICD-RxJS normal tests and performances tests are all passed without any problem.