FIR IDE: move low level api testdata sources to the analysis directory

analysis/low-level-api-fir/testdata/fileStructure/localFun.kt

@@ -0,0 +1,13 @@
+fun x() {/* ReanalyzableFunctionStructureElement */
+    fun y() {
+
+    }
+}
+
+class A {/* NonReanalyzableDeclarationStructureElement */
+    fun z() {/* ReanalyzableFunctionStructureElement */
+        fun q() {
+
+        }
+    }
+}