`@validate()` decorator should support multi-line lambda expressions

**Is your feature request related to a problem? Please describe.**

In the [request for enhancement](https://github.com/Azure/bicep-reps/blob/790a3ab7b6ae8a1c1fff2097ac34719d60a16f0a/active/0010-custom-validation-decorators.md#client-side-changes), there's an example provided by Jonny on a multi-line lambda expression on the `@validate()` decorator:

```bicep
@validate(
x => startsWith(x, 'fo'), 'baz must start with the letters \'fo\'',
x => endsWith(x, 'd'), 'baz must end with the letter \'d\'',
x => length(x) == 4, 'baz be exactly 4 letters')
param baz string
```

Now, using the latest version (v0.38.5), multi-line support is not available.

**Describe the solution you'd like**

Allow multi-line lambda expression for the `@validate()` decorator.

Start by reproducing the multi-line @validate() example from the issue on Bicep v0.38.5 and trace how lambda expressions in decorators are parsed. The work is done when the shown decorator with multiple lines is accepted and existing single-line validation behavior remains intact.

Written by the indexing model from the issue text.