[FIX] reactivity: only show key in subscription if observed by callback

Previously, the getSubscriptions debugging utility returned all observed
keys for a given target, instead of only the keys observed by the
callback it received as argument. This commit fixes that issues.

tests/components/__snapshots__/reactivity.test.ts.snap

@@ -140,3 +140,39 @@ exports[`reactivity in lifecycle state changes in willUnmount do not trigger rer
   }
 }"
 `;
+
+exports[`subscriptions subscriptions returns the keys and targets observed by the component 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(ctx['state'].a);
+  }
+}"
+`;
+
+exports[`subscriptions subscriptions returns the keys observed by the component 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  const comp1 = app.createComponent(\`Child\`, true, false, false, false);
+  
+  return function template(ctx, node, key = \\"\\") {
+    const b2 = text(ctx['state'].a);
+    const b3 = comp1({state: ctx['state']}, key + \`__1\`, node, this, null);
+    return multi([b2, b3]);
+  }
+}"
+`;
+
+exports[`subscriptions subscriptions returns the keys observed by the component 2`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(ctx['props'].state.b);
+  }
+}"
+`;