Using custom functions through desiredStateConfiguration targetScope does not work

[Gijsreyn]

Bicep version
Bicep CLI version 0.37.4 (27cc8db)

Describe the bug
Microsoft DSC v3 implements its own custom functions. For example, to determine the current drive, I could define the following:

targetScope = 'desiredStateConfiguration'

resource powerShellAdapter 'PSDesiredStateConfiguration/File@2025-01-07' = {
  name: 'Use Bicep to create file'
  properties: {
        Ensure: 'Present'
        Type: 'File'
        DestinationPath: '${systemroot()}\\DSC\\config.txt'
        Contents: 'This file was created using Bicep extension from DSC.'
    }
}

Trying to compile this, results in an error:

To Reproduce
Grab the example from the pull request and run bicep build file_with_condition.dsc.bicep

Additional context
Add any other context about the problem here.

[SydneyhSmith]

@andyleejordan @SteveL-MSFT @mgreenegit @theJasonHelmick fyi