JS(extractor): support optional chaining

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -1077,4 +1077,8 @@ xmllocations(
 
 @dataflownode = @expr | @functiondeclstmt | @classdeclstmt | @namespacedeclaration | @enumdeclaration | @property;
 
-/* Last updated 2017/07/11. */
+@optionalchainable = @callexpr | @propaccess;
+
+isOptionalChaining(int id: @optionalchainable ref);
+
+/* Last updated 2018/10/22. */

javascript/ql/src/semmlecode.javascript.dbscheme.stats

@@ -1393,6 +1393,10 @@
 <k>@xmlcharacters</k>
 <v>439958</v>
 </e>
+<e>
+<k>@optionalchainable</k>
+<v>100</v>
+</e>
 </typesizes>
 <stats>
 <relation>
@@ -19773,6 +19777,18 @@
 </columnsizes>
 <dependencies/>
 </relation>
+<relation>
+<name>isOptionalChaining</name>
+<cardinality>100</cardinality>
+<columnsizes>
+<e>
+<k>id</k>
+<v>100</v>
+</e>
+</columnsizes>
+<dependencies/>
+</relation>
+
 <relation>
 <name>rangeQuantifierLowerBound</name>
 <cardinality>146</cardinality>