[FE 1.0] Improve error message for disabled "Unit conversions" feature

^KT-49394 Fixed

compiler/frontend.common-psi/src/org/jetbrains/kotlin/diagnostics/rendering/LanguageFeatureMessageRenderer.kt

@@ -12,6 +12,9 @@ class LanguageFeatureMessageRenderer @JvmOverloads constructor(
     private val type: Type,
     private val useHtml: Boolean = false
 ) : DiagnosticParameterRenderer<Pair<LanguageFeature, LanguageVersionSettings>> {
+    private val additionalFeatureMessages = mapOf(
+        LanguageFeature.UnitConversionsOnArbitraryExpressions to "You can also change the original type of this expression to (...) -> Unit"
+    )
 
     enum class Type {
         UNSUPPORTED,
@@ -52,6 +55,10 @@ class LanguageFeatureMessageRenderer @JvmOverloads constructor(
             }
         }
 
+        if (feature in additionalFeatureMessages) {
+            sb.append(". ${additionalFeatureMessages[feature]}")
+        }
+
         return sb.toString()
     }
 }

compiler/testData/diagnostics/tests/unitConversion/kt49394.kt

@@ -11,5 +11,5 @@ val x = {
 }
 
 fun test() {
-    handle(<!UNSUPPORTED_FEATURE("The feature "unit conversions on arbitrary expressions" is experimental and should be enabled explicitly")!>x<!>)
+    handle(<!UNSUPPORTED_FEATURE("The feature "unit conversions on arbitrary expressions" is experimental and should be enabled explicitly. You can also change the original type of this expression to (...) -> Unit")!>x<!>)
 }