Simplify type mapping logic in CodegenBinding

- inline asmType to calling getAsmType, which does something more
- refactor getJvmInternalName to use getAsmType as well
- simplify getAsmType and fix a probable bug in mapping singletons nested in
  enums (which wasn't reproduced, though a test is added)
- delete unnnecessary ASM_TYPE recording for enum entries in
  CodegenAnnotatingVisitor

compiler/testData/codegen/box/enum/objectInEnum.kt

@@ -0,0 +1,20 @@
+enum class E {
+    ENTRY
+    SUBCLASS {
+        object O {
+            fun foo() = 2
+        }
+        override fun bar() = O.foo()
+    }
+
+    object O {
+        fun foo() = 1
+    }
+    open fun bar() = O.foo()
+}
+
+fun box(): String {
+    if (E.ENTRY.bar() != 1) return "Fail 1"
+    if (E.SUBCLASS.bar() != 2) return "Fail 2"
+    return "OK"
+}