JS: Avoid scanning individual comment lines to find generated code markers

Some subclasses of GeneratedCodeMarkerComment regex match against `getLine(_)`.
When evaluated, this results in multiple scans (one per subclass that uses it)
of all comment lines in the database, before regex matching against those lines.

To make these scans smaller, regex match against the entire comment text
without splitting them into lines.
This is achieved using `?m` (multiline) and line boundaries in the regexes.

Author: adityasharad

javascript/ql/lib/semmle/javascript/GeneratedCode.qll

@@ -49,14 +49,14 @@ private predicate codeGeneratorMarkerComment(Comment c, string tool) {
  */
 private class GenericGeneratedCodeMarkerComment extends GeneratedCodeMarkerComment {
   GenericGeneratedCodeMarkerComment() {
-    exists(string line | line = getLine(_) |
-      exists(string entity, string was, string automatically |
-        entity = "code|file|class|interface|art[ei]fact|module|script" and
-        was = "was|is|has been" and
-        automatically = "automatically |mechanically |auto[- ]?" and
-        line.regexpMatch("(?i).*\\b(This|The following) (" + entity + ") (" + was + ") (" +
-            automatically + ")?gener(e?)ated\\b.*")
-      )
+    exists(string entity, string was, string automatically |
+      entity = "code|file|class|interface|art[ei]fact|module|script" and
+      was = "was|is|has been" and
+      automatically = "automatically |mechanically |auto[- ]?" and
+      // Look for this pattern in each line of the comment.
+      this.getText()
+          .regexpMatch("(?im)^.*\\b(This|The following) (" + entity + ") (" + was + ") (" +
+              automatically + ")?gener(e?)ated\\b.*$")
     )
   }
 }
@@ -66,9 +66,14 @@ private class GenericGeneratedCodeMarkerComment extends GeneratedCodeMarkerComme
  */
 private class DontModifyMarkerComment extends GeneratedCodeMarkerComment {
   DontModifyMarkerComment() {
-    exists(string line | line = getLine(_) |
-      line.regexpMatch("(?i).*\\bGenerated by\\b.*\\bDo not edit\\b.*") or
-      line.regexpMatch("(?i).*\\bAny modifications to this file will be lost\\b.*")
+    exists(string pattern |
+      // Look for these patterns in each line of the comment.
+      this.getText().regexpMatch(pattern) and
+      pattern =
+        [
+          "(?im)^.*\\bGenerated by\\b.*\\bDo not edit\\b.*$",
+          "(?im)^.*\\bAny modifications to this file will be lost\\b.*$"
+        ]
     )
   }
 }