refactor: convert TaskLayoutOptions to enum

[ilandikov]

Description

• convert TaskLayoutOptions to enum
• remove a place to edit when adding new Task field (// NEW_TASK_FIELD_EDIT_REQUIRED)
• replace Task fields string values with references to enum

Motivation and Context

• create a single container for TaskLayoutOptions value
• strengthen the code by having links to values instead of values
• decrease number of places to edit when adding new Task field (// NEW_TASK_FIELD_EDIT_REQUIRED)

How has this been tested?

Unit tests.

Types of changes

Internal changes:

• Refactor (prefix: refactor - non-breaking change which only improves the design or structure of existing code, and making no changes to its external behaviour)
• Tests (prefix: test - additions and improvements to unit tests and the smoke tests)

Checklist

• My code follows the code style of this project and passes yarn run lint.
• My change has adequate Unit Test coverage.

Terms

• My contribution follow this project's contributing guide
• I agree to follow this project's Code of Conduct

[claremacrae]

I went to rename Task.blockedBy to Task.dependsOn - and realised it would conflict with this, so have held off doing it for now.