[KT-58817] Implicit import issues cannot be reported

To be reported with [1] imports require source. It was missing for
implicit script imports.

`FirScriptConfiguratorExtensionImpl` was extended and now adds fake
source elements (users don't see imports in the source code).

Since diagnostics for implicit import statements are meaningless for
IDE, they are suppressed in `LLFirDiagnosticReporter`.

----------------------------------------------------------------------
[1]: DiagnosticReporter.reportOn()

compiler/frontend.common/src/org/jetbrains/kotlin/KtSourceElement.kt

@@ -272,6 +272,9 @@ sealed class KtFakeSourceElementKind(final override val shouldSkipErrorTypeRepor
 
     // When property doesn't have an initializer and explicit return type, but its getter's return type is specified
     object PropertyTypeFromGetterReturnType : KtFakeSourceElementKind()
+
+    // Scripts get implicit imports from their configurations
+    object ImplicitImport : KtFakeSourceElementKind()
 }
 
 sealed class AbstractKtSourceElement {