Rename test data folder: libraries -> decompiler

idea/testData/decompiler/navigation/fromLibSource/Foo.kt

@@ -0,0 +1,3 @@
+package a
+
+class Foo

idea/testData/decompiler/navigation/fromLibSource/usage.kt

@@ -0,0 +1,6 @@
+package b
+
+import a.*
+
+fun doSomething(f: Foo, t: Thread, s: String) {
+}