[JS IR] Materialize Unit more aggressively for IrCalls

Unit materialization for IrCall is required for operations with dynamic type.

However it produces useless Unit_getInstance() calls,
especially in return expressions. The pach also adds some heuristics
for reducing the amount of Unit_getInstance() calls from return expressions:
do not add Unit_getInstance() if return value has Unit type.

Relaited to KT-51139
^KT-23252 Fixed

js/js.translator/testData/box/coercion/unitMaterializationOnAssign.kt

@@ -0,0 +1,51 @@
+// DONT_TARGET_EXACT_BACKEND: JS
+// KJS_WITH_FULL_RUNTIME
+
+fun demo(): Unit {}
+
+fun testFunctionUsage() {
+    val u1 = demo()
+    val d1: dynamic = u1
+    assertTrue(d1 == u1)
+    assertEquals(u1.toString(), "kotlin.Unit")
+}
+
+fun testFunctionCall() {
+    fun test(u1: Unit): Boolean {
+        val d1: dynamic = u1
+        assertEquals(u1.toString(), "kotlin.Unit")
+        return d1 == u1
+    }
+    assertTrue(test(demo()))
+}
+
+fun testObjectField() {
+    val o = object { val u1 = demo() }
+    val d1: dynamic = o.u1
+    assertTrue(d1 == o.u1)
+    assertEquals(o.u1.toString(), "kotlin.Unit")
+}
+
+fun testClassField() {
+    class Test(val u1: Unit)
+    val o = Test(demo())
+    val d1: dynamic = o.u1
+    assertTrue(d1 == o.u1)
+    assertEquals(o.u1.toString(), "kotlin.Unit")
+}
+
+fun testContainer() {
+    val l = listOf<Unit>(demo())
+    val d1: dynamic = l.last()
+    assertTrue(d1 == l.last())
+    assertEquals(l.last().toString(), "kotlin.Unit")
+}
+
+fun box(): String {
+    testFunctionUsage()
+    testFunctionCall()
+    testObjectField()
+    testClassField()
+    testContainer()
+    return "OK"
+}