csharp: Generating documentation for tuple-value properties.

csharp: Generating documentation for tuple-value properties.

Adds documentation for tuple-value properties (properties with
multiple values), so the following Eo:

```
@property multi_valued_prop {
   [[ A multi valued property. ]]
   get {}
   set {}
   values {
     prop1: int; [[ Dummy property's first element. ]]
     prop2: int; [[ Dummy property's second element. ]]
   }
}
```

Generates the following documentation:

```
/// <summary>A multi valued property.<br/>
/// Since EFL *current version*.</summary>
/// <value>A tuple containing the following information:
/// <list type="bullet">
/// <item><description><c>prop1</c> (<c>Item0</c>): Dummy property&apos;s first element.</description></item>
/// <item><description><c>prop2</c> (<c>Item1</c>): Dummy property&apos;s second element.</description></item>
/// </list></value>
```

Note: This commit also adds a default separator between tag name and
parameters in `generate_opening_tag`.

Ref T8468.

Differential Revision: https://phab.enlightenment.org/D10889