[FIR] Infer Unit type for generic lambda function if implicit return exists

Make behavior more consistent with K1

^KT-63563 Fixed

compiler/testData/diagnostics/tests/functionLiterals/return/LambdaReturnTypeIsUnitIfImplicitReturnExists.kt

@@ -0,0 +1,22 @@
+// FIR_IDENTICAL
+// ISSUE: KT-63563
+
+fun foo(x: () -> Any) = x()
+fun foo2(x: () -> Unit) = x()
+fun <T> foo3(x: () -> T): T = x()
+
+fun main2() {
+    foo {
+        if ("0".hashCode() == 42) <!RETURN_TYPE_MISMATCH!>return@foo<!>
+        ""
+    }
+    foo2 {
+        if ("1".hashCode() == 42) return@foo2
+        ""
+    }
+    foo3 { // Infer T to Unit -> no error
+        if ("2".hashCode() == 42) return@foo3
+        ""
+    }
+}
+

compiler/testData/diagnostics/tests/functionLiterals/return/LocalReturnNoCoercionToUnit.fir.kt

@@ -1,6 +0,0 @@
-fun test(a: Int) {
-    run f@{
-      if (a > 0) <!RETURN_TYPE_MISMATCH!>return@f<!>
-      else return@f 1
-    }
-}

compiler/testData/diagnostics/tests/functionLiterals/return/LocalReturnNoCoercionToUnit.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 fun test(a: Int) {
     run f@{
       if (a > 0) return@f

compiler/testData/diagnostics/tests/functionLiterals/return/LocalReturnUnitAndDontCareType.fir.kt

@@ -1,20 +0,0 @@
-// NI_EXPECTED_FILE
-val flag = true
-
-// type of a was checked by txt
-val a = run { // () -> Unit
-    return@run
-}
-
-// Unit
-val b = run {
-    if (flag) return@run
-    5
-}
-
-// Unit
-val c = run {
-    if (flag) <!RETURN_TYPE_MISMATCH!>return@run<!>
-
-    return@run 4
-}

compiler/testData/diagnostics/tests/functionLiterals/return/LocalReturnUnitAndDontCareType.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // NI_EXPECTED_FILE
 val flag = true