Keep track of array types in OptimizationBasicInterpreter

Merging array types with different element types, for example
`[Lj/l/String;` and `[Lj/l/Object;`, now produces `[Lj/l/Object;`
(instead of `Lj/l/Object;`), which allows for more precise tracking of
null values because we assume that AALOAD on a non-array typed value is
possible only if that value is null.

 #KT-54802 Fixed

compiler/testData/codegen/box/casts/kt54802.kt

@@ -0,0 +1,14 @@
+class K {
+    val x: String = "OK"
+}
+
+inline fun <T> Array<out T>.ifEmpty(body: () -> Array<out T>): Array<out T> =
+    if (size == 0) body() else this
+
+inline fun <T> Array<out T>.f(p: (T) -> String): String =
+    p(this[0])
+
+fun box(): String =
+    emptyArray<K>()
+        .ifEmpty { arrayOf(K()) }
+        .f(K::x)