PSI2IR: Unify behavior for lambda return values with old back-end

See KT-35849.

1. When expected lambda return type is a type parameter, don't generate
introduce implicit casts (even if the corresponding type parameter has
an upper bound that would otherwise require such cast).

2. Do not generate implicit null check for lambda return value of
@EnhancedNullability type.

compiler/testData/codegen/box/javaInterop/notNullAssertions/enhancedNullability/inLambdaReturnWithExpectedType.kt

@@ -0,0 +1,64 @@
+// !LANGUAGE: +StrictJavaNullabilityAssertions
+// TARGET_BACKEND: JVM
+
+// FILE: inLambdaReturnWithExpectedType.kt
+fun check(fn: () -> Any) { fn() }
+
+fun <T> checkT(fn: () -> T) { fn() }
+
+fun <T : Any> checkTAny(fn: () -> T) { fn() }
+
+fun box(): String {
+    // TODO language design; see KT-35849
+
+    try {
+        check { J().nullString() }
+        throw AssertionError("Fail: 'check { J().nullString() }' should throw")
+    } catch (e: Throwable) {
+    }
+
+    try {
+        check { J().notNullString() }
+        throw AssertionError("Fail: 'check { J().notNullString() }' should throw")
+    } catch (e: Throwable) {
+    }
+
+    try {
+        checkT { J().nullString() }
+    } catch (e: Throwable) {
+        throw AssertionError("Fail: 'checkT { J().nullString() }' should not throw")
+    }
+
+    try {
+        checkT { J().notNullString() }
+    } catch (e: Throwable) {
+        throw AssertionError("Fail: 'checkT { J().notNullString() }' should not throw")
+    }
+
+    try {
+        checkTAny { J().nullString() }
+    } catch (e: Throwable) {
+        throw AssertionError("Fail: 'checkTAny { J().nullString() }' should not throw")
+    }
+
+    try {
+        checkTAny { J().notNullString() }
+    } catch (e: Throwable) {
+        throw AssertionError("Fail: 'checkTAny { J().notNullString() }' should not throw")
+    }
+
+    return "OK"
+}
+
+// FILE: J.java
+import org.jetbrains.annotations.NotNull;
+
+public class J {
+    public String nullString() {
+        return null;
+    }
+
+    public @NotNull String notNullString() {
+        return null;
+    }
+}