KT-29862 startOffset of class declaration

NB startOffset of primary class constructor declaration should still
point to the 'class' keyword (because of debugger requirements).

compiler/testData/ir/sourceRanges/declarations/kt29862.kt

@@ -0,0 +1,15 @@
+abstract class Test1(
+    val x: Int
+) {
+}
+
+public
+abstract
+class Test2(
+    val x: Int
+) {
+    inner
+    class TestInner(
+        val x: Int
+    )
+}