Add test for method reference whose LHS has unknown type

This can happen when imports or source classes are missing.

Author: smowton

java/ql/test/library-tests/unknown-method-reference-lhs/Diags.expected

@@ -0,0 +1,2 @@
+| Test.java:0:0:0:0 | 1 |
+| Test.java:4:13:4:30 | Unable to extract method reference Unavailable.f()::g with no owner type |

java/ql/test/library-tests/unknown-method-reference-lhs/Diags.ql

@@ -0,0 +1,4 @@
+import java
+import semmle.code.java.Diagnostics
+
+select any(Diagnostic d | not d.toString().matches("Not rewriting trap file for%"))

java/ql/test/library-tests/unknown-method-reference-lhs/Test.java

@@ -0,0 +1,7 @@
+public class Test {
+
+  public static void test() {
+    var x = Unavailable.f()::g;
+  }
+
+}

java/ql/test/library-tests/unknown-method-reference-lhs/options

@@ -0,0 +1 @@
+//semmle-extractor-options: --no-strict-javac-errors --javac-args -source 17 -target 17