FIR IDE: Add ability in test infra to have a "before" file different in

FIR vs FE1.0, and made file naming convention more consistent.

idea/testData/quickfix/replaceWithSafeCall/functionExpressionBody.fir.kt.after

@@ -0,0 +1,8 @@
+// "Replace with safe (?.) call" "true"
+// WITH_RUNTIME
+// ERROR: Type mismatch: inferred type is Int? but Int was expected
+
+// Note: There should be no error in FIR but errors are not currently checked for FIR
+class T {
+    fun foo(s: String?): Int = s?.length ?: <caret>
+}