Add build mode tests (ensuring isDevelopingApp and isTesting are appropriately true when they need to be (as well as assert-stripping))

[NullVoxPopuli]

followup to: #64

Key changes:

• tell vitest to not forward its env to our invoked ember-cli / test commands
• add babel-plugin-debug-macros for @glimmer/env for DEBUG support (only for the dev/test babel.config)
• in the tests/index.html, enable the embroider-macros sync of isTesting via importing @embroider/macros/src/vendor/embroider-macros-test-support

[NullVoxPopuli]

could be PR'd separately

[NullVoxPopuli]

extendEnv is noise in this PR without an accompanying env: {} to set the env to empty

[mkszepp]

Would be nice to get this PR

In ember-basic-dropdown i have isTesting() in use, which isn't working right now without adding a workaround in test-helpers start() function

[mkszepp]

@NullVoxPopuli the fix of this branch works only partially...

I have an issue found out with ember-power-select and ember-basic-dropdown.
The ember-basic-dropdown addon has two isTesting() points (see here, this is the more critical point, when it stays false while testing).

When the ember-power-select is using the workaround from this branch, isTesting() is inside the ember-power-select addon true in test, but in ember-basic-dropdown code parts it's always false, which is not expected.

If you run this in ember app test (like ember-power-select docs), isTesting() is true, which is expected.

If you want test this issue, you can do this with following steps.

1. Download ember-power-select (https://github.com/cibernox/ember-power-select)
2. Run pnpm i
3. Insert a console.log(isTesting()); in node_modules/ember-basic-dropdown/dist/components/basic-dropdown.js
4. Run pnpm test on root or pnpm start with http://localhost:4200/tests

The isTesting() is always false and so all tests will normally fail. I have only added a workaround in eps, by setting destination (https://github.com/cibernox/ember-power-select/blob/master/tests/test-helper.ts#L51-L54, normaly this should not be needed)