Link out to wiki page for the concept of a "generator" (#2985)

* Remove version-specific syntax description about expressing a list of enumerators

* Replace 'filter' with 'guard' for consistency

* Link to the book for clarification of generator and guard control structures

* Clarify what a 'generator' is in a couple of spots

* Update _tour/for-comprehensions.md

---------

Co-authored-by: Ali Hong <alih@netflix.com>
Co-authored-by: Jamie Thompson <bishbashboshjt@gmail.com>

Author: 3 people

_overviews/scala3-book/control-structures.md

@@ -236,7 +236,7 @@ for i <- ints do println(i)
 {% endtabs %}
 
 
-The code `i <- ints` is referred to as a _generator_.
+The code `i <- ints` is referred to as a _generator_. In any generator `p <- e`, the expression `e` can generate zero or many bindings to the pattern `p`.
 
 This is what the result looks like in the Scala REPL:
 

_overviews/scala3-book/taste-control-structures.md

@@ -92,7 +92,8 @@ val ints = List(1, 2, 3, 4, 5)
 for (i <- ints) println(i)
 ```
 
-> The code `i <- ints` is referred to as a _generator_, and the code that follows the closing parentheses of the generator is the _body_ of the loop.
+> The code `i <- ints` is referred to as a _generator_. In any generator `p <- e`, the expression `e` can generate zero or many bindings to the pattern `p`.
+> The code that follows the closing parentheses of the generator is the _body_ of the loop.
 
 {% endtab %}
 

_tour/for-comprehensions.md

@@ -12,7 +12,7 @@ redirect_from:
   - "/tutorials/tour/sequence-comprehensions.html"
 ---
 
-Scala offers a lightweight notation for expressing _sequence comprehensions_. Comprehensions have the form `for (enumerators) yield e`, where `enumerators` refers to a semicolon-separated list of enumerators. An _enumerator_ is either a generator which introduces new variables, or it is a filter. A comprehension evaluates the body `e` for each binding generated by the enumerators and returns a sequence of these values.
+Scala offers a lightweight notation for expressing _sequence comprehensions_. Comprehensions have the form `for (enumerators) yield e`, where `enumerators` refers to a list of enumerators. An _enumerator_ is either a generator, or it is a guard (see: [Control Structures](/scala3/book/control-structures.html#for-loops)). A comprehension evaluates the body `e` for each binding generated by the enumerators and returns a sequence of these values.
 
 Here's an example: