TypeScript: support syntax for optional tuple type elements

javascript/ql/src/semmle/javascript/TypeScript.qll

@@ -1073,6 +1073,14 @@ class IsTypeExpr extends @istypeexpr, TypeExpr {
   TypeExpr getPredicateType() { result = this.getChildTypeExpr(1) }
 }
 
+/**
+ * An optional type element in a tuple type, such as `number?` in `[string, number?]`.
+ */
+class OptionalTypeExpr extends @optionaltypeexpr, TypeExpr {
+  /** Gets the type `T` in `T?` */
+  TypeExpr getElementType() { result = getChildTypeExpr(0) }
+}
+
 /**
  * A possibly qualified name that refers to a variable from inside a type.
  *

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -556,7 +556,9 @@ case @typeexpr.kind of
 | 29 = @infertypeexpr
 | 30 = @importtypeaccess
 | 31 = @importnamespaceaccess
-| 32 = @importvartypeaccess;
+| 32 = @importvartypeaccess
+| 33 = @optionaltypeexpr
+;
 
 @typeref = @typeaccess | @typedecl;
 @typeidentifier = @typedecl | @localtypeaccess | @typelabel | @localvartypeaccess | @localnamespaceaccess;