Report diagnostic on import with explicit import class if class was imported earlier.

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

@@ -0,0 +1,48 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+// FILE: 1.kt
+package a
+
+class someFun() {}
+fun someFun(i: Int) {}
+
+class someVal() {}
+val Int.someVal: Int get() = 3
+
+class A
+
+class B
+
+// FILE: 2.kt
+package b
+
+class someFun
+class someVal
+class someAll
+
+fun A() {}
+
+class B
+
+
+// FILE: 3.kt
+import a.<!CONFLICTING_IMPORT!>someFun<!>
+import b.<!CONFLICTING_IMPORT!>someFun<!>
+
+import a.<!CONFLICTING_IMPORT!>someVal<!>
+import b.<!CONFLICTING_IMPORT!>someVal<!>
+
+import a.A
+import b.A
+
+// FILE: 4.kt
+import b.*
+import a.B
+
+// FILE: 5.kt
+package b
+
+import a.B
+
+// FILE: 6.kt
+import a.<!CONFLICTING_IMPORT!>B<!>
+import b.<!CONFLICTING_IMPORT!>B<!>