JS: Model readline as a stdin threat-model source

Technically not always true, but my assumption is that +90% of the time
that's what it will be used for, so while we could be more precise by
adding a taint-step from the `input` part of the construction, I'm not
sure it's worth it in this case.

Furthermore, doing so would break with the current way we model
threat-model sources, and how sources are generally modeled in JS... so
for a very pretty setup it would require changing all the other `file`
threat-model sources to start at the constructors such as
`fs.createReadStream()` and have taint-propagation steps towards the
actual use (like we do in Python)...

I couldn't see an easy path forwards for doing this while keeping the
Concepts integration, so I opted for the simpler solution here.

javascript/ql/lib/semmle/javascript/frameworks/NodeJSLib.model.yml

@@ -8,3 +8,5 @@ extensions:
       - ['fs', 'Member[promises].Member[readFile].ReturnValue.Member[then].Argument[0].Parameter[0]', 'file']
       - ['global', 'Member[process].Member[stdin].Member[read].ReturnValue', 'stdin']
       - ['global', 'Member[process].Member[stdin].Member[on,addListener].WithStringArgument[0=data].Argument[1].Parameter[0]', 'stdin']
+      - ['readline', 'Member[createInterface].ReturnValue.Member[question].Argument[1].Parameter[0]', 'stdin']
+      - ['readline', 'Member[createInterface].ReturnValue.Member[on,addListener].WithStringArgument[0=line].Argument[1].Parameter[0]', 'stdin']

javascript/ql/test/library-tests/threat-models/sources/sources.js

@@ -84,10 +84,10 @@ SINK(data); // $ hasFlow
 // using readline
 const readline = require('readline');
 const rl_file = readline.createInterface({
-    input: fs.createReadStream('file.txt') // $ MISSING: threat-source=file
+    input: fs.createReadStream('file.txt')
 });
-rl_file.on("line", (line) => {
-    SINK(line); // $ MISSING: hasFlow
+rl_file.on("line", (line) => { // $ SPURIOUS: threat-source=stdin MISSING: threat-source=file
+    SINK(line); // $ hasFlow
 });
 
 
@@ -104,17 +104,17 @@ SINK(stdin_line); // $ hasFlow
 // Accessing stdin using readline
 const readline = require('readline');
 const rl_stdin = readline.createInterface({
-    input: process.stdin // $ MISSING: threat-source=stdin
+    input: process.stdin
 });
-rl_stdin.question('<question>', (answer) => {
-    SINK(answer); // $ MISSING: hasFlow
+rl_stdin.question('<question>', (answer) => { // $ threat-source=stdin
+    SINK(answer); // $ hasFlow
 });
 
-function handler(answer) {
-    SINK(answer); // $ MISSING: hasFlow
+function handler(answer) { // $ threat-source=stdin
+    SINK(answer); // $ hasFlow
 }
 rl_stdin.question('<question>', handler);
 
-rl_stdin.on("line", (line) => {
-    SINK(line); // $ MISSING: hasFlow
+rl_stdin.on("line", (line) => { // $ threat-source=stdin
+    SINK(line); // $ hasFlow
 });