FIR IDE: do not use IJ test infrastructure in frontend-api-fir tests

compiler/test-infrastructure-utils/tests/org/jetbrains/kotlin/test/Assertions.kt

@@ -6,12 +6,17 @@
 package org.jetbrains.kotlin.test
 
 import java.io.File
+import java.nio.file.Path
 
 abstract class Assertions {
     fun assertEqualsToFile(expectedFile: File, actual: String, sanitizer: (String) -> String = { it }) {
         assertEqualsToFile(expectedFile, actual, sanitizer) { "Actual data differs from file content" }
     }
 
+    fun assertEqualsToFile(expectedFile: Path, actual: String, sanitizer: (String) -> String = { it }) {
+        assertEqualsToFile(expectedFile.toFile(), actual, sanitizer)
+    }
+
     abstract fun assertEqualsToFile(
         expectedFile: File,
         actual: String,