FIR IDE: move validation contract to analysis session base class

idea/idea-frontend-api/src/org/jetbrains/kotlin/idea/frontend/api/FrontendAnalysisSession.kt

@@ -5,11 +5,17 @@
 
 package org.jetbrains.kotlin.idea.frontend.api
 
+import com.intellij.openapi.project.Project
 import org.jetbrains.kotlin.diagnostics.Diagnostic
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.psi.*
 
-abstract class FrontendAnalysisSession : Invalidatable {
+abstract class FrontendAnalysisSession(project: Project) : Invalidatable {
+    protected val validityToken = ReadActionConfinementValidityToken(project)
+    override fun isValid(): Boolean = validityToken.isValid()
+    override fun invalidationReason(): String = validityToken.invalidationReason()
+
+
     abstract fun getSmartCastedToTypes(expression: KtExpression): Collection<TypeInfo>?
 
     abstract fun getImplicitReceiverSmartCasts(expression: KtExpression): Collection<ImplicitReceiverSmartCast>

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/FirAnalysisSession.kt

@@ -33,12 +33,8 @@ import org.jetbrains.kotlin.psi.*
 
 class FirAnalysisSession(
     project: Project
-) : FrontendAnalysisSession() {
-    private val validityToken = ReadActionConfinementValidityToken(project)
-    override fun isValid(): Boolean = validityToken.isValid()
-    override fun invalidationReason(): String = validityToken.invalidationReason()
-
-    constructor(element: KtElement) : this(element.project)
+) : FrontendAnalysisSession(project) {
+   constructor(element: KtElement) : this(element.project)
 
     init {
         assertIsValid()