[BUGFIX stable] Fix type dependency issues

Add `@simple-dom/interface` and `@glimmer/syntax` to `dependencies` so
they are present in the graph for consumers who will not be getting
them transitively from the `@glimmer/*` deps which are pre-built into
Ember. (Medium-term, it would be preferable for our type emit to roll
up these kinds of dependencies the same way Ember's build does *or* for
Ember's build to stop rolling them up; whichever we choose, the goal
will be for them to *match*.)

Fixes #20479.

package.json

@@ -71,8 +71,10 @@
     "@glimmer/program": "0.84.2",
     "@glimmer/reference": "0.84.2",
     "@glimmer/runtime": "0.84.2",
+    "@glimmer/syntax": "0.84.2",
     "@glimmer/validator": "0.84.2",
     "@glimmer/vm-babel-plugins": "0.84.2",
+    "@simple-dom/interface": "^1.4.0",
     "babel-plugin-debug-macros": "^0.3.4",
     "babel-plugin-filter-imports": "^4.0.0",
     "backburner.js": "^2.7.0",