Added tests.

Author: DanielRosenwasser

tests/cases/conformance/expressions/typeAssertions/duplicatePropertiesInTypeAssertions01.ts

@@ -0,0 +1,3 @@
+// @declaration: true
+
+let x = <{a: number; a: number}>{};

tests/cases/conformance/expressions/typeAssertions/duplicatePropertiesInTypeAssertions02.ts

@@ -0,0 +1,3 @@
+// @declaration: true
+
+let x = {} as {a: number; a: number};