FE1.0/FIR: add test for "double import" situation

compiler/testData/diagnostics/tests/imports/DoubleImports.kt

@@ -0,0 +1,41 @@
+// FILE: StarImported.kt
+
+package star
+
+class SomeClass
+
+fun foo() {}
+
+val bar = 1
+
+// FILE: ExplicitImported.kt
+
+package explicit
+
+class AnotherClass
+
+fun baz() {}
+
+val gau = 2
+
+// FILE: Test.kt
+
+import star.*
+import star.*
+import explicit.<!CONFLICTING_IMPORT!>AnotherClass<!>
+import explicit.<!CONFLICTING_IMPORT!>AnotherClass<!>
+import explicit.baz
+import explicit.baz
+import explicit.gau
+import explicit.gau
+
+fun useSomeClass(): SomeClass = SomeClass()
+
+fun useAnotherClass(): AnotherClass = AnotherClass()
+
+fun test() {
+    foo()
+    baz()
+    val x = bar
+    val y = gau
+}