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;

javascript/ql/test/library-tests/TypeScript/Types/UnknownType.expected

@@ -0,0 +1 @@
+| tst.ts:40:5:40:15 | unknownType | unknown |

javascript/ql/test/library-tests/TypeScript/Types/UnknownType.ql

@@ -0,0 +1,5 @@
+import javascript
+
+from Expr e
+where e.getType() instanceof UnknownType
+select e, e.getType()

javascript/ql/test/library-tests/TypeScript/Types/tst.ts

@@ -32,3 +32,9 @@ const uniqueSymbolType: unique symbol = null;
 let objectType: object;
 let intersection: string & {x: string};
 let tuple: [number, string];
+
+let tupleWithOptionalElement: [number, string, number?];
+let emptyTuple: [];
+let tupleWithRestElement: [number, ...string[]];
+let tupleWithOptionalAndRestElements: [number, string?, ...number[]];
+let unknownType: unknown;