Add if() function

[SteveL-MSFT]

PR Summary

Add the if() function needed for Bicep support

PR Context

Part of #767

[andyleejordan]

Amazing, this now works:

Q:\src\DSC\bin\debug\dsc.exe -l debug config --parameters '{"parameters": {"colorMode": "light"}}' set --file .\demo.json

with this ternary in Bicep:

@allowed(['light', 'dark'])
@description('Light or dark color mode')
// TODO: Teach DSC how to use Bicep param files
param colorMode string = 'light'

var valueData = colorMode == 'light' ? 1 : 0

var keyPathPrefix = 'HKCU\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion'

resource systemUsesLightTheme 'Microsoft.Windows/Registry@2025-04-07' = {
    name: 'SystemUsesLightTheme'
    properties: {
        keyPath: concat(keyPathPrefix, '\\Themes\\Personalize')
        valueName: 'SystemUsesLightTheme'
        valueData: {
          DWord: valueData
        }
    }
}