TypeScript: support unknown static type

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

@@ -2188,6 +2188,11 @@ class TupleType extends ArrayType, @tupletype {
  */
 class AnyType extends Type, @anytype {}
 
+/**
+ * The predefined `unknown` type.
+ */
+class UnknownType extends Type, @unknowntype {}
+
 /**
  * The predefined `string` type.
  */

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -610,6 +610,7 @@ case @type.kind of
 | 20 = @thistype
 | 21 = @numberliteraltype
 | 22 = @stringliteraltype
+| 23 = @unknowntype
 ;
 
 @booleanliteraltype = @truetype | @falsetype;