Code Quality: Create an `IsNetFramework` or equivalent switch to determine target frameworks

### Description

There should be a `IsNetFramework`, `IsNetStandard`, `IsNetFx` and `IsNetCore` switch that determines the target framework.

### Concerned code

- `eng/`

### Gains

- Easier to track target frameworks for capabilities

### Requirements

- Create a new file called `TfmTracking.props`
- Add logic to set switch based on property

### Comments

_No response_