Synchronized IdeFirProvider.getOrBuild file, don't share RawFirBuilder

Before this commit RawFirBuilder was reused,
that provoked a lot of synchronization problems

idea/idea-analysis/src/org/jetbrains/kotlin/idea/fir/FirIdeJavaModuleBasedSession.kt

@@ -9,7 +9,6 @@ import com.intellij.openapi.project.Project
 import com.intellij.psi.search.GlobalSearchScope
 import org.jetbrains.kotlin.analyzer.ModuleInfo
 import org.jetbrains.kotlin.fir.FirModuleBasedSession
-import org.jetbrains.kotlin.fir.builder.RawFirBuilder
 import org.jetbrains.kotlin.fir.java.FirProjectSessionProvider
 import org.jetbrains.kotlin.fir.java.JavaSymbolProvider
 import org.jetbrains.kotlin.fir.resolve.FirProvider
@@ -32,7 +31,7 @@ class FirIdeJavaModuleBasedSession(
     init {
         registerComponent(
             FirProvider::class,
-            IdeFirProvider(project, scope, RawFirBuilder(this, stubMode = false), this)
+            IdeFirProvider(project, scope, this)
         )
         registerComponent(
             FirSymbolProvider::class,

idea/idea-analysis/src/org/jetbrains/kotlin/idea/fir/IdeFirProvider.kt

@@ -28,7 +28,6 @@ import org.jetbrains.kotlin.psi.KtFile
 class IdeFirProvider(
     val project: Project,
     val scope: GlobalSearchScope,
-    val builder: RawFirBuilder,
     val session: FirSession
 ) : FirProvider() {
     private val cacheProvider = FirProviderImpl(session)
@@ -51,10 +50,13 @@ class IdeFirProvider(
     }
 
     fun getOrBuildFile(ktFile: KtFile): FirFile {
-        return files.getOrPut(ktFile) {
-            val file = builder.buildFirFile(ktFile)
-            cacheProvider.recordFile(file)
-            file
+        files[ktFile]?.let { return it }
+        return synchronized(ktFile) {
+            files.getOrPut(ktFile) {
+                val file = RawFirBuilder(session, stubMode = false).buildFirFile(ktFile)
+                cacheProvider.recordFile(file)
+                file
+            }
         }
     }