Wrong diagnostic when last expression in lambda contains assignment operation

#KT-6769 Fixed

compiler/testData/diagnostics/tests/functionLiterals/assignmentOperationInLambda.kt

@@ -0,0 +1,16 @@
+fun test(bal: Array<Int>) {
+    var bar = 4
+
+    val a = { bar += 4 }
+    a : () -> Unit
+
+    val b = { bar = 4 }
+    b : () -> Unit
+
+    val c = { bal[2] = 3 }
+    c : () -> Unit
+
+    val d = run { bar += 4 }
+    d : Unit
+}
+fun <T> run(f: () -> T): T = f()

compiler/testData/diagnostics/tests/functionLiterals/assignmentOperationInLambda.txt

@@ -0,0 +1,4 @@
+package
+
+internal fun </*0*/ T> run(/*0*/ f: () -> T): T
+internal fun test(/*0*/ bal: kotlin.Array<kotlin.Int>): kotlin.Unit

compiler/testData/diagnostics/tests/functionLiterals/assignmentOperationInLambdaWithExpectedType.kt

@@ -0,0 +1,16 @@
+fun test(bal: Array<Int>) {
+    var bar = 4
+
+    val <!UNUSED_VARIABLE!>a<!>: () -> Unit = { bar += 4 }
+
+    val <!UNUSED_VARIABLE!>b<!>: () -> Int = { <!EXPECTED_TYPE_MISMATCH!>bar = 4<!> }
+
+    val <!UNUSED_VARIABLE!>c<!>: () -> <!UNRESOLVED_REFERENCE!>UNRESOLVED<!> = { bal[2] = 3 }
+
+    val <!UNUSED_VARIABLE!>d<!>: () -> Int = { <!ASSIGNMENT_TYPE_MISMATCH(kotlin.Int)!>bar += 4<!> }
+
+    val <!UNUSED_VARIABLE!>e<!>: Unit = run { bar += 4 }
+
+    val <!UNUSED_VARIABLE!>f<!>: Int = <!TYPE_INFERENCE_EXPECTED_TYPE_MISMATCH!>run<!> { bar += 4 }
+}
+fun <T> run(f: () -> T): T = f()

compiler/testData/diagnostics/tests/functionLiterals/assignmentOperationInLambdaWithExpectedType.txt

@@ -0,0 +1,4 @@
+package
+
+internal fun </*0*/ T> run(/*0*/ f: () -> T): T
+internal fun test(/*0*/ bal: kotlin.Array<kotlin.Int>): kotlin.Unit

compiler/testData/diagnostics/tests/functionLiterals/kt6869.kt

@@ -0,0 +1,11 @@
+fun main(args : Array<String>) {
+    var list = listOf(1)
+
+    val a: Int? = 2
+
+    a?.let { list += it }
+}
+
+fun <T : Any, R> T.let(f: (T) -> R): R = f(this)
+fun <T> Iterable<T>.plus(<!UNUSED_PARAMETER!>element<!>: T): List<T> = null!!
+fun listOf<T>(vararg <!UNUSED_PARAMETER!>values<!>: T): List<T> = null!!

compiler/testData/diagnostics/tests/functionLiterals/kt6869.txt

@@ -0,0 +1,6 @@
+package
+
+internal fun </*0*/ T> listOf(/*0*/ vararg values: T /*kotlin.Array<out T>*/): kotlin.List<T>
+internal fun main(/*0*/ args: kotlin.Array<kotlin.String>): kotlin.Unit
+internal fun </*0*/ T : kotlin.Any, /*1*/ R> T.let(/*0*/ f: (T) -> R): R
+internal fun </*0*/ T> kotlin.Iterable<T>.plus(/*0*/ element: T): kotlin.List<T>