Java: Introduce LoC summary metric query

java/ql/src/Metrics/Summaries/LinesOfCode.ql

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+/**
+ * @id java/summary/lines-of-code
+ * @name Total lines of code in the database
+ * @description The total number of lines of code across all files. This is a useful metric of the size of a database.
+ *              For all files that were seen during the build, this query counts the lines of code, excluding whitespace
+ *              or comments.
+ * @kind metric
+ * @tags summary
+ */
+
+import java
+
+select sum(File f, int i | i = f.getNumberOfLinesOfCode() | i)

java/ql/test/query-tests/Metrics/A.java

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+public class A {
+  public void M() {
+    //some comment
+  }
+
+  /* public void M() {
+    //some comment
+  } */
+}

java/ql/test/query-tests/Metrics/LinesOfCode.expected

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+| 4 |

java/ql/test/query-tests/Metrics/LinesOfCode.qlref

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+Metrics/Summaries/LinesOfCode.ql