Add OptionalValue declarations to each of the non-Swift targets, so that

this can be used in the test templates.

It is a no-op for every target other than Swift.

This pairs with cset 8251422b.

runtime-testsuite-legacy/resources/org/antlr/v4/test/runtime/templates/LeftRecursion/MultipleAlternativesWithCommonLabel.stg

@@ -35,5 +35,3 @@ INC : '++' ;
 DEC : '--' ;
 WS : (' '|'\n') -> skip;
 >>
-
-/* other targets'.test.stg added:  OptionalValue(value) ::= "<value>"  */

runtime-testsuite/resources/org/antlr/v4/test/runtime/templates/Chrome.test.stg

@@ -278,7 +278,6 @@ Declare_pred() ::= <<this.pred = function(v) {
 >>
 
 Invoke_pred(v) ::= <<this.pred(<v>)>>
-
 ContextRuleFunction(ctx, rule) ::= "<ctx>.<rule>"
 StringType() ::= "String"
 ContextMember(ctx, subctx, member) ::= "<ctx>.<subctx>.<member>"

runtime-testsuite/resources/org/antlr/v4/test/runtime/templates/Go.test.stg

@@ -332,7 +332,6 @@ func pred(v bool) bool {
 >>
 
 Invoke_pred(v) ::= <<pred(<v>)>>
-
 ContextRuleFunction(ctx, rule) ::= "<ctx>.<rule>"
 StringType() ::= "String"
 ContextMember(ctx, subctx, member) ::= "<ctx>.<subctx>.<member; format={cap}>"