Loops not supported in variable definition with ternary operator

**Bicep version**
v0.6.18

**Describe the bug**
Cannot define a variable with a ternary operator and a loop being used in one of the operator arguments.

**To Reproduce**
```bicep
var foo = true ? [for i in range(0,10): i] : []
output fooout array = foo
```

>For-expressions are not supported in this context. For-expressions may be used as values of resource, module, variable, and output declarations, or values of resource and module properties.bicep(BCP138)

Start by compiling the reproduction in the issue with Bicep v0.6.18 and trace the diagnostic that rejects the for-expression inside the ternary operator. Determine the compiler behavior needed for this expression to compile, then verify that the reproduction succeeds without regressing the existing for-expression restrictions.

Written by the indexing model from the issue text.