Cache virtualFilePath for KtFile

Because of com.intellij.openapi.vfs.local.CoreLocalVirtualFile#getPath
that has a rather slow implementation calling String::replace on each call

At the same time this method gets called very frequently when
recording lookups

compiler/frontend/src/org/jetbrains/kotlin/incremental/KotlinLookupLocation.kt

@@ -32,7 +32,7 @@ class KotlinLookupLocation(val element: KtElement) : LookupLocation {
             if (containingJetFile.doNotAnalyze != null) return null
 
             return object : LocationInfo {
-                override val filePath = containingJetFile.virtualFile.path
+                override val filePath = containingJetFile.virtualFilePath
 
                 override val position: Position
                     get() = getLineAndColumnInPsiFile(containingJetFile, element.textRange).let { Position(it.line, it.column) }

compiler/frontend/src/org/jetbrains/kotlin/psi/KtFile.kt

@@ -50,6 +50,9 @@ open class KtFile(viewProvider: FileViewProvider, val isCompiled: Boolean) :
     @Volatile
     private var hasTopLeveCallables: Boolean? = null
 
+    @Volatile
+    private var pathCached: String? = null
+
     val importList: KtImportList?
         get() = findChildByTypeOrClass(KtStubElementTypes.IMPORT_LIST, KtImportList::class.java)
 
@@ -104,6 +107,15 @@ open class KtFile(viewProvider: FileViewProvider, val isCompiled: Boolean) :
             return result
         }
 
+    val virtualFilePath
+        get(): String {
+            pathCached?.let { return it }
+
+            return virtualFile.path.also {
+                pathCached = it
+            }
+        }
+
     val isScriptByTree: Boolean
         get() = script != null
 
@@ -170,6 +182,7 @@ open class KtFile(viewProvider: FileViewProvider, val isCompiled: Boolean) :
         super<PsiFileBase>.clearCaches()
         isScript = null
         hasTopLeveCallables = null
+        pathCached = null
     }
 
     fun isScript(): Boolean = stub?.isScript() ?: isScriptByTree