[PSI2IR] Propagate smart cast information for variable loads.

This gives us more precise type information and can enable backend
optimizations. This was motivated by when expressions not compiled
to table switches in the JVM_IR backend.

Fixed KT-36845.

compiler/testData/codegen/bytecodeText/whenEnumOptimization/kt14597_full.kt

@@ -1,6 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-// TODO KT-36845 Generate enum-based TABLESWITCH/LOOKUPSWITCH on a value with smart cast to enum in JVM_IR
-
 enum class En { A, B, С }
 
 fun box() {

compiler/testData/codegen/bytecodeText/whenEnumOptimization/kt14802.kt

@@ -1,6 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-// TODO KT-36845 Generate enum-based TABLESWITCH/LOOKUPSWITCH on a value with smart cast to enum in JVM_IR
-
 class EncapsulatedEnum<T : Enum<T>>(val value: T)
 
 enum class MyEnum(val value: String) {