Support the TC39 pipeline operator

Summary

Implement the Stage 2 TC39 proposal: https://github.com/tc39/proposal-pipeline-operator

Implement the current proposal exactly: topic syntax, precedence, associativity, early errors, evaluation order, and await/yield interactions.

Why

This proposal fits GocciaScript's modern ECMAScript surface and the 0.13.0 proposal roadmap. It should extend the engine's existing architecture rather than arrive as a userland shim.

Current behavior

No pipeline expression or topic-reference syntax exists.

Expected behavior

Implement the current proposal exactly: topic syntax, precedence, associativity, early errors, evaluation order, and await/yield interactions.

Scope notes

Treat the live proposal as authoritative; do not support legacy variants. Add dedicated AST/bytecode lowering after #875, evaluating each stage once and preserving suspension/scopes. Cover arrows, calls, optional chains, ASI adjacency, docs, formatting, and tests. Additive syntax: no flag.

Related bytecode roadmap: #871 and #875. Update the relevant language/built-in documentation and Goccia proposal inventory. Use the proposal repository and its current specification at implementation time; add focused project tests and matching pinned Test262/proposal coverage without regressions.

Acceptance criteria

• Parser/API surface, descriptors, evaluation order, errors, and observable protocol behavior match the current proposal.
• Implementation uses the identified shared engine seam without a duplicate compatibility shim.
• Focused positive, negative, abrupt-completion, and edge-case tests cover the proposal.
• Relevant project suites, pinned Test262 cases, formatting, and documentation checks pass.

Start with the current TC39 pipeline-operator proposal and the bytecode roadmap issues #871 and #875, then locate the shared engine seam for AST and bytecode lowering. Review the existing parser, evaluator, suspension, and scope tests before adding focused proposal, Test262, formatting, and documentation coverage. Done means the current proposal’s syntax, errors, evaluation behavior, and await/yield interactions pass the project and pinned proposal suites.