add tests for exception tracking on externals

Author: tsnobip

tests/analysis_tests/tests-reanalyze/deadcode/expected/exception.txt

@@ -91,5 +91,9 @@
   Exception Analysis
   ExnA.res:1:5-7
   bar might raise Not_found (ExnA.res:1:16) and is not annotated with @raises(Not_found)
+
+  Exception Analysis
+  ExternalTest.res:7:5-24
+  bigIntFromStringExn2 might raise Exn.Error (ExternalTest.res:7:35) and is not annotated with @raises(Exn.Error)
 
-  Analysis reported 23 issues (Exception Analysis:23)
+  Analysis reported 24 issues (Exception Analysis:24)

tests/analysis_tests/tests-reanalyze/deadcode/src/exception/ExternalTest.res

@@ -0,0 +1,7 @@
+@raises(Exn.Error)
+external bigIntFromStringExn: string => bigint = "BigInt"
+
+@raises(Exn.Error)
+let bigIntFromStringExn = s => s->bigIntFromStringExn
+
+let bigIntFromStringExn2 = s => s->bigIntFromStringExn