Convert GraphQLID to RestID when fetching project data in WebIDE

What does this MR do and why?

Context

When fetching a project’s data, the WebIDE uses two endpoints: REST API and GraphQL API. Then it combines both objects. Now that we are fetching an object’s ID on every GraphQL query, the GraphQL id overwrote the ID coming from the REST ID which broke the expectation of other API requests, in particular, fetching merge requests and branches.

See incident channel #incident-5997 in slack: https://gitlab.slack.com/archives/C02PATX8L9Z

Solution

This MR converts the GraphQL ID to a numeric value as expected by other rest APIs.

Screenshots or screen recordings

How to set up and validate locally

Open the WebIDE and try changing the current branch or Merge Request

MR acceptance checklist

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