Publish types in public-types with typesVersions

Publish types to a `public-types` directory, in parallel to the
in-place Babel-powered emit for JS. In the future, we should probably
go ahead and remove the Babel emit and get this the rest of the way
into a v2 addon format with a single publish step. However, this
minimizes the delta introduced in this particular PR, and thus keeps
the risk lower.

This does *not* correctly publish types for `ember-test-helpers`.
However, there remains only one export from that package the
`has-ember-version` module and helper, which is also available from
`@ember/test-helpers`. Accordingly, we can simply ignore that (and plan
to go ahead and eventually remove it).

.gitignore

@@ -28,3 +28,4 @@
 # tyescript related output files
 addon-test-support/**/*.js
 addon-test-support/**/*.d.ts
+public-types

package.json

@@ -23,7 +23,10 @@
     "test": "tests"
   },
   "scripts": {
-    "prepack": "yarn babel --extensions '.ts' --presets @babel/preset-typescript addon-test-support --out-dir addon-test-support/ --ignore '**/*.d.ts'",
+    "build:types": "tsc",
+    "build:js": "yarn babel --extensions '.ts' --presets @babel/preset-typescript addon-test-support --out-dir addon-test-support/ --ignore '**/*.d.ts'",
+    "build": "npm-run-all --parallel build:*",
+    "prepack": "yarn build",
     "postpack": "rimraf addon-test-support/**/*.js",
     "clean": "git clean -x -f",
     "docs": "documentation build --document-exported \"addon-test-support/@ember/test-helpers/index.js\" --config documentation.yml --markdown-toc-max-depth 3 -f md -o API.md",
@@ -152,5 +155,12 @@
   "volta": {
     "node": "12.22.4",
     "yarn": "1.22.4"
+  },
+  "typesVersions": {
+    "*": {
+      "*": [
+        "public-types/*"
+      ]
+    }
   }
 }

tsconfig.json

@@ -1,6 +1,11 @@
 {
   "extends": "@tsconfig/ember/tsconfig.json",
   "compilerOptions": {
+    // Use TS to emit declarations
+    "noEmit": false,
+    "emitDeclarationOnly": true,
+    "outDir": "public-types",
+
     "paths": {
       "dummy/tests/*": ["./tests/*"],
       "dummy/*": ["./tests/dummy/app/*", "./app/*"],