Update visualstudio.js to handle custom project field

[brentonrace]

🌟 What does this PR do?

Updated visualstudio.js to handle custom project field if it exists on the work item page, otherwise fall back to current logic to find project.

🐛 Recommendations for testing

• In Azure DevOps, customize work item layout for a given work item type (e.g. PBI or Bug) to include a custom field called "Project", and add some custom values.
• Open a PBI of that type in the work item screen and select a value in the Project dropdown.
• Confirm when clicking the Toggl button, the value from the dropdown is used to populate Project on the time entry.

All changes should be tested across Chrome and Firefox.