Add test for extraction of a Java file with a non-UTF-8 charset

Author: smowton

java/ql/test/library-tests/comment-encoding/PrintAst.expected

@@ -0,0 +1,3 @@
+Test.java:
+#    0| [CompilationUnit] Test
+#    1|   1: [Class] Test

java/ql/test/library-tests/comment-encoding/PrintAst.qlref

@@ -0,0 +1 @@
+semmle/code/java/PrintAst.ql

java/ql/test/library-tests/comment-encoding/Test.java

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+public class Test {
+}
+
+// ÄãºÃÊÀ½ç

java/ql/test/library-tests/comment-encoding/options

@@ -0,0 +1 @@
+//semmle-extractor-options: --encoding GBK

java/ql/test/library-tests/comment-encoding/toString.expected

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+| Test.java:4:1:4:7 | // \u4f60\u597d\u4e16\u754c |

java/ql/test/library-tests/comment-encoding/toString.ql

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+import java
+
+from Javadoc c
+select c