Add rfc931: 'native' option to preserve template() in output

[NullVoxPopuli-ai-agent]

Summary

Adds an rfc931 option that controls how the RFC 931 template() API (imported from @ember/template-compiler) is emitted:

• "polyfilled" (default) — existing behavior. template() is lowered to the older, widely-supported primitives (precompileTemplate / createTemplateFactory plus setComponentTemplate and templateOnly) so the output runs on Ember versions that don't natively understand template().
• "native" — the template() call is preserved in the output, for runtimes that implement @ember/template-compiler natively (Ember 6+). AST transforms still run, and the implicit eval form is normalized into the explicit scope form.

// input
import { template } from '@ember/template-compiler';
import HelloWorld from 'somewhere';
export default template('<HelloWorld />', { eval() { return eval(arguments[0]); } });

// output with { targetFormat: 'hbs', rfc931: 'native' }
import { template } from '@ember/template-compiler';
import HelloWorld from 'somewhere';
export default template('<HelloWorld />', { scope: () => ({ HelloWorld }) });

Findings / design notes

I read through RFC 931, the discussion thread, the existing plugin, the in-progress draft #109, and ember-source's native implementation of @ember/template-compiler. Key conclusions that shaped the design:

1. template() only ever takes a string. ember-source's native template(templateString, options) calls glimmerPrecompile(templateString, ...) at runtime — it never accepts a precompiled wire factory. So "preserving template()" is only meaningful when the body stays as an HBS string, i.e. targetFormat: 'hbs'.

2. targetFormat: 'wire' needs no special native handling. The standard wire output — setComponentTemplate(createTemplateFactory(...), component ?? templateOnly()) — is exactly what native template() produces internally, and it already runs on native runtimes. Wrapping a wire factory back into a template() call would not execute on Ember (it expects a string). So rfc931: 'native' only changes hbs-target output; in wire it falls back to the normal compiled form.

3. eval → scope normalization is the useful work in native mode. The implicit (eval) form is the intermediate emitted by content-tag; converting it to the explicit scope form (via the existing implicit ScopeLocals machinery + updateScope) produces the canonical, statically-analyzable, publishable form. component and the user's strict option are preserved untouched; eval is dropped.

Implementation

• The @ember/template-compiler module config's rfc931Support now resolves to the user's rfc931 choice ('polyfilled' | 'native') in configuredModules.
• updateCallForm (the hbs path) gains a native branch that keeps the template() callee and its import, drops eval, and lets updateScope append the explicit scope.
• wire path and import cleanup are unchanged.

Tests

Adds a native rfc931 suite covering: template-only and class-backed components (static block + out-of-class component:), eval→scope conversion, strict preservation, multiple templates per module, no-options template-only, and the wire fallback. Full suite: 137 passing, lint clean.

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