Move lateinit assertion for companion property to companion object

Previously, for a property named `x` in the companion object of a class
named `Foo`, we generated:
- `Foo.access$getX$cp`, consisting of `GETFIELD Foo.x` and lateinit
  assertion
- `Foo.Companion.getX`, consisting of `INVOKEVIRTUAL Foo.access$getX$cp`

Now, we generate:
- `Foo.access$getX$cp`, consisting of `GETFIELD Foo.x`
- `Foo.Companion.getX`, consisting of `INVOKEVIRTUAL Foo.access$getX$cp`
  and lateinit assertion

The reason is that this way we can avoid generating another accessor and
reuse `Foo.access$getX$cp` in case `isInitialized` is called on a
lateinit property from companion.

For private properties, getX is not generated, but instead the assertion
is generated on each access to the field (which can be improved, see
KT-28331). The same happens for access to non-private properties from
inside the same context where they're declared.

 #KT-21862 In Progress

compiler/testData/codegen/bytecodeText/properties/lateinit/companionObject.kt

@@ -0,0 +1,24 @@
+class Foo {
+    private companion object {
+        lateinit var x: String
+
+        fun test() {
+            consume(x)
+            consume(x)
+            consume(x)
+            consume(x)
+        }
+    }
+
+    fun test2() {
+        consume(x)
+        consume(x)
+        consume(x)
+        consume(x)
+    }
+}
+
+fun consume(s: String) {}
+
+// There's 1 assertion in Foo.Companion.getX, and 4 in Foo.test2 (see KT-28331)
+// 5 throwUninitializedPropertyAccessException

compiler/testData/codegen/bytecodeText/properties/lateinit/companionObjectFromLambda.kt

@@ -0,0 +1,20 @@
+class Foo {
+    private companion object {
+        lateinit var x: String
+
+        fun test() {
+            consume({ x }());
+            { consume(x) }()
+        }
+    }
+
+    fun test2() {
+        consume({ x }());
+        { consume(x) }()
+    }
+}
+
+fun consume(s: String) {}
+
+// There's only one assertion in Foo.Companion.getX
+// 1 throwUninitializedPropertyAccessException