Add lines-of-code tags

This is a proposed method for advertising which queries are measuring
the lines of code in a project in a more robust manner than inspecting
the rule id.

Note that the python "LinesOfUserCode" query should _not_ have this
property, as otherwise the results of the two queries will be summed.

javascript/ql/src/Summary/LinesOfCode.ql

@@ -4,6 +4,7 @@
  * @description The total number of lines of JavaScript or TypeScript code across all files checked into the repository, except in `node_modules`. This is a useful metric of the size of a database. For all files that were seen during extraction, this query counts the lines of code, excluding whitespace or comments.
  * @kind metric
  * @tags summary
+ *       lines-of-code
  */
 
 import javascript