Optimize coercion to Unit.

POP operations are backward-propagated.

Operation can't be transformed if its result is moved within stack
(by DUP, DUP_X1, DUP_X2, DUP2, DUP2_X1, DUP2_X2, or SWAP).

Unnecessary operations are replaced with NOPs (for debugger).
Unnecessary NOPs are removed.

KT-9922 Suboptimal generation for simple safe call with unused return value
KT-11116 Optimize methods returning Unit

compiler/testData/codegen/bytecodeText/coercionToUnitOptimization/nopInlineFuns.kt

@@ -0,0 +1,26 @@
+fun test() {
+    val a = inlineFunInt { 1 }
+    val b = simpleFunInt { 1 }
+    val c = inlineFunVoid { val aa = 1 }
+    val d = simpleFunVoid { val aa = 1 }
+}
+
+inline fun inlineFunInt(f: () -> Int): Int {
+    val a = 1
+    return f()
+}
+
+inline fun inlineFunVoid(f: () -> Unit): Unit {
+    val a = 1
+    return f()
+}
+
+fun simpleFunInt(f: () -> Int): Int {
+    return f()
+}
+
+fun simpleFunVoid(f: () -> Unit): Unit {
+    return f()
+}
+
+// 3 NOP