PLAYLIST::Id: convert to enum class

[notspiff]

Description

Converter int type and loose values to proper enum class

Motivation and context

While there is a lot of casting to int, at least everything is explicitly cast and confirmed by
the compiler now.

How has this been tested?

It builds.

What is the effect on users?

None

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• Student submission (PR was done for educational purposes and will be treated as such)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[garbear]

Love the change.

So strong... the bikeshedding beckons... I like capital ID 🙂 What does our style guide say?

[notspiff]

it says, you want that tint on your shed, you do it.

[garbear]

Toss some paint on it and call it a day. Id is good.