RFC#560 - {{eq}}, {{neq}} as keywords

[NullVoxPopuli-ai-agent]

Summary

Implements RFC #560 — adds eq and neq as new helpers and strict-mode keywords.

• Implements two equality helpers as plain functions in @glimmer/runtime
• eq uses strict equality (===), neq uses strict inequality (!==)
• Re-exports from @ember/helper with YUIDoc and Opaque type interfaces
• Registers as keywords in the template compiler (strict-mode only, not available in loose mode)
• Each helper throws in DEBUG mode if not called with exactly two arguments

New files

• packages/@glimmer/runtime/lib/helpers/{eq,neq}.ts — helper implementations
• packages/@glimmer-workspace/integration-tests/test/keywords/{eq,neq}-test.ts — tests with explicit scope
• packages/@glimmer-workspace/integration-tests/test/keywords/{eq,neq}-runtime-test.ts — runtime keyword tests

Modified files

• packages/@glimmer/runtime/index.ts — exports
• packages/@ember/helper/index.ts — re-exports with docs
• packages/@ember/template-compiler/lib/compile-options.ts — keyword registration
• packages/@ember/template-compiler/lib/plugins/auto-import-builtins.ts — AST rewriting
• smoke-tests/scenarios/basic-test.ts — gjs smoke test
• tests/docs/expected.js — docs coverage allowlist

Test plan

• eq: equal numbers, unequal numbers, equal strings
• neq: unequal numbers, equal numbers
• Runtime keyword tests (explicit scope, eval, no scope)
• DEBUG arity error tests
• Smoke test

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