Eliminate redundant CHECKCAST instructions

CHECKCAST is redundant if the corresponding static type exactly matches the target type.
CHECKCAST instructions to-be-reified should not be eliminated.

KT-14811 Unnecessary checkcast generated in parameterized functions
KT-14963 unnecessary checkcast java/lang/Object

compiler/testData/codegen/bytecodeText/boxingOptimization/checkcastAndInstanceOf.kt

@@ -20,4 +20,4 @@ fun bar() {
 // 0 valueOf
 // 0 Value\s\(\)
 // 2 INSTANCEOF
-// 2 CHECKCAST
+// 1 CHECKCAST

compiler/testData/codegen/bytecodeText/checkcast/kt14811.kt

@@ -0,0 +1,12 @@
+interface WorldObject {
+    val name: String
+}
+
+fun testB(worldObj: WorldObject) {
+    val y = worldObj.let {
+        println("object name: ${it.name}")
+        it
+    }
+}
+
+// 0 CHECKCAST

compiler/testData/codegen/bytecodeText/checkcast/kt14963.kt

@@ -0,0 +1,3 @@
+fun <T> f(o: Any): T = o as T
+
+// 0 CHECKCAST