False positive `no-undef` for template-imports and contextual components

[simonihmig]

This is failing linting with form and field "locals" (they are not local to the outer template scope, so not supposed to be provided by JS scope, which ESLint thinks here) falsely violating no-undef:

<template>
  <HeadlessForm @data={{data}} as |form|>
    <form.field @name="firstName" as |field|>
      <field.label>First Name</field.label>
      <field.input data-test-first-name />
    </form.field>
    <form.field @name="lastName" as |field|>
      <field.label>Last Name</field.label>
      <field.input data-test-last-name />
    </form.field>
  </HeadlessForm>
</template>

I think I have identified the root cause in @glimmer/syntax, keeping this for tracking. /cc @NullVoxPopuli

[simonihmig]

My attempt to fix this upstream: https://github.com/glimmerjs/glimmer-vm/pull/1406

[bmish]

Note that this change was reverted:

• https://github.com/ember-cli/eslint-plugin-ember/pull/1920
• https://github.com/ember-cli/eslint-plugin-ember/pull/1941