[FIR-TEST] Move existing contract tests to fromLibrary directory

compiler/fir/analysis-tests/testData/resolveWithStdlib/contracts/fromLibrary/notIsNullOrEmpty.kt

@@ -0,0 +1,14 @@
+fun test_1(s: String?) {
+    when {
+        !s.isNullOrEmpty() -> s.length // Should be OK
+    }
+}
+
+fun test_2(s: String?) {
+    // contracts related
+    if (s.isNullOrEmpty()) {
+        s.<!INAPPLICABLE_CANDIDATE!>length<!> // Should be bad
+    } else {
+        s.length // Should be OK
+    }
+}