string-interpolation: the raw-interpolator also performs variable substitution

Clarify that the raw-interpolator also performs variable
substitution. This was not obvious from the text and it is easy to
believe that raw means just that: the raw string, as is, without any
substitutions performed.

This also moves the last sentence of the raw-interpolator section
into the following section, where it logicaly belongs.

Author: Flowdalic

_overviews/scala3-book/string-interpolation.md

@@ -211,6 +211,20 @@ res1: String = a\nb
 
 The raw interpolator is useful when you want to avoid having expressions like `\n` turn into a return character.
 
+Furthermore, the raw interpolator allows the usage of variables, which are replaced with their value, just as the s interpolator.
+
+{% tabs example-11 %}
+{% tab 'Scala 2 and 3' for=example-11 %}
+```scala
+scala> val foo = 42
+scala> raw"a\n$foo"
+res1: String = a\n42
+```
+{% endtab %}
+{% endtabs %}
+
+## Advanced Usage
+
 In addition to the three default string interpolators, users can define their own.
 
 ## Advanced Usage
@@ -224,8 +238,8 @@ here's a quick example to help illustrate how they work.
 
 In Scala, all processed string literals are simple code transformations. Anytime the compiler encounters a processed string literal of the form:
 
-{% tabs example-11 %}
-{% tab 'Scala 2 and 3' for=example-11 %}
+{% tabs example-12 %}
+{% tab 'Scala 2 and 3' for=example-12 %}
 ```scala
 id"string content"
 ```