Fix incorrect Github REST API response types

[IzN432]

Summary:

Fixes #1314

Changes Made:

• Added GithubRestIssue, a type to accept issue responses from the REST API
• Replaced the type GithubIssue with GithubRestIssue where relevant
• Added a factory method in GithubIssue to convert GithubRestIssue to GithubIssue

Proposed Commit Message:

Add type to correctly process issues from the REST API

Issue responses from the REST API are being accepted as the GithubIssue
class. This is incorrectly typed since the REST API returns a lower
cased state, while GithubIssue expects an upper cased state.

This causes an inconsistency when updating the issues in
issue.service.ts with the response from these REST API queries, which
is done during close and reopen. This prevents us from filtering based
on the state correctly.

Let's add a new type called GithubRestIssue that accurately represents
the issue response from the REST API. We then add a factory method in
GithubIssue that creates a GithubIssue from a GithubRestIssue and
replace all incorrect GithubIssue usages with GithubRestIssue.

[yucongkoo]

After some code tracing, there is a RestGithubIssueState type in github-issue-filter.model.ts:

I think it would be better to reuse this type instead of hard coding the state values here

[Eclipse-Dominator]

Good work on the factory function. Now restoring and deleting issues is nearly instant!

I noticed you missed some replacing some GithubIssue in some areas but it does not change any functionalities as neither the state field or the issue was accessed by the rest of the program.

Thus, I will approve this but I'll let you decide if you wish to change them.

1. toFetchIssue
2. getIssuesAPICall (this is binded w toFetchIssues)

[IzN432]

Updated toFetchIssues and getIssuesAPICall as well as toFetchIssue and the IssueCacheManager methods

[Eclipse-Dominator]

LGTM!