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

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

@@ -0,0 +1,9 @@
+fun a() {/* ReanalyzableFunctionStructureElement */
+    class X
+}
+
+class Y {/* NonReanalyzableDeclarationStructureElement */
+    fun b() {/* ReanalyzableFunctionStructureElement */
+        class Z
+    }
+}