[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()

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostics/LLFirDiagnosticReporter.kt

@@ -7,6 +7,8 @@ package org.jetbrains.kotlin.analysis.low.level.api.fir.diagnostics
 
 import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.AbstractKtSourceElement
+import org.jetbrains.kotlin.KtFakeSourceElement
+import org.jetbrains.kotlin.KtFakeSourceElementKind
 import org.jetbrains.kotlin.analysis.low.level.api.fir.util.addValueFor
 import org.jetbrains.kotlin.diagnostics.*
 
@@ -18,6 +20,10 @@ internal class LLFirDiagnosticReporter : DiagnosticReporter() {
         if (diagnostic == null) return
         if (context.isDiagnosticSuppressed(diagnostic)) return
 
+        // Implicit imports for scripts are currently implemented via FIR-tree mutation (they do not exist in default importing scopes).
+        // So as a temporary solution we filter out related diagnostics here.
+        if (diagnostic.isAboutImplicitImport()) return
+
         val psiDiagnostic = when (diagnostic) {
             is KtPsiDiagnostic -> diagnostic
             is KtLightDiagnostic -> diagnostic.toPsiDiagnostic()
@@ -51,6 +57,10 @@ internal class LLFirDiagnosticReporter : DiagnosticReporter() {
     }
 }
 
+private fun KtDiagnostic.isAboutImplicitImport() =
+    (element is KtFakeSourceElement && (element as KtFakeSourceElement).kind == KtFakeSourceElementKind.ImplicitImport)
+
+
 private fun KtLightDiagnostic.toPsiDiagnostic(): KtPsiDiagnostic {
     val psiSourceElement = element.unwrapToKtPsiSourceElement()
         ?: error("Diagnostic should be created from PSI in IDE")