make examples for is dynamic look parallel (#4687)

* make examples for `is dynamic` look parallel

In particular, put both inside a block.

* rearrange example with twigil `$*x` accordingly

* add link to /language/variables#The_*_twigil

* add ling to /type/Variable#trait_is_dynamic

* clarify that this section is only about *pre-defined* dynamic variables

Author: schultzdavid

doc/Language/variables.rakudoc

@@ -300,11 +300,12 @@ my $*FOO = 'bar';
 say foo; # OUTPUT: «bar␤»
 =end code
 
+See also L<trait is dynamic|/type/Variable#trait_is_dynamic>.
+
 Dynamic variables can have lexical scope when declared with C<my> or package
 scope when declared with C<our>. Dynamic resolution and resolution through
 symbol tables introduced with C<our> are two orthogonal issues.
 
-
 X<|Syntax,$?>X<|Syntax,?>X<|Syntax,$?>X<|Syntax,@?>X<|Syntax,%?>X<|Syntax,&?>
 =head2 The C<?> twigil
 
@@ -1524,8 +1525,8 @@ sub get-file-content {
 
 =head2 Dynamic variables
 
-All dynamically scoped variables have the C<*> twigil, and their name is
-(conventionally) written in uppercase.
+The pre-defined dynamically scoped variables all have the L<C<*> twigil|#The_*_twigil>,
+and their name is (conventionally) written in uppercase.
 
 X<|Variables,$*ARGFILES>X<|Variables,@*ARGS>
 =head3 Argument related variables
@@ -1866,7 +1867,7 @@ To activate this only for a lexical scope:
 my $*RAT-OVERFLOW = FatRat;
 =end code
 
-How does that work? The $*RAT-OVERFLOW variable is supposed to contain
+How does that work? The C<$*RAT-OVERFLOW> variable is supposed to contain
 a class or instance on which the C<UPGRADE-RAT> method will be called
 when a Rat overflows. So you can introduce your own behavior by
 creating a class with an C<UPGRADE-RAT> method in it.

doc/Type/Variable.rakudoc

@@ -60,28 +60,30 @@ without being in an inner lexical scope.
 sub introspect() {
     say $CALLER::x;
 }
-my $x is dynamic = 23;
-introspect;         # OUTPUT: «23␤»
 {
-    # not dynamic
-    my $x;
-    introspect()    # dies with an exception of X::Caller::NotDynamic
+    my $x is dynamic = 42;
+    introspect();  # OUTPUT: «42␤»
+}
+{
+    my $x = 41;    # not dynamic
+    introspect();  # dies with an exception of X::Caller::NotDynamic
 }
 =end code
 
 The C<is dynamic> trait is a rather cumbersome way of creating and accessing
-dynamic variables.  A much easier way is to use the C<* twigil>:
+dynamic variables.  A much easier way is to use the L<C<* twigil>|/language/variables#The_*_twigil>:
 
 =begin code
 sub introspect() {
     say $*x;
 }
-my $*x = 23;
-introspect;         # OUTPUT: «23␤»
 {
-    # not dynamic
-    my $x;
-    introspect()    # dies with an exception of X::Dynamic::NotFound
+    my $*x = 42;
+    introspect();  # OUTPUT: «42␤»
+}
+{
+    my $x = 41;    # not dynamic
+    introspect();  # dies with an exception of X::Dynamic::NotFound
 }
 =end code