compat-eslint: SyntheticLazyNode base — architectural boundary for synthetic intermediates

[johnsoncodehk]

Summary

• Closes the last drift path in the lazy ESTree shim. Synthetic intermediates (nodes with no direct TS counterpart, like TSTypeAnnotation / ClassBody / ChainExpression-wrapper) used to opt out of map registration via a registerInMaps=false constructor flag. Easy to forget when adding a new synthetic class — and a forgotten one produces silently-wrong parent references on bottom-up materialise.
• Replace the boolean with SyntheticLazyNode, an abstract base that overrides _registersInMaps() to return false. The 14 synthetic-creating classes now extend SyntheticLazyNode instead of extend LazyNode. Adding a 15th is a visible architectural act in code review.
• JSXOpeningElementNode is hybrid (synthetic only when wrapping a JsxSelfClosingElement) — keeps LazyNode base but overrides _registersInMaps() based on this._ts.kind, so the synthetic constructor arg is gone too.
• Also drops a dead registerInMaps param on JSXIdentifierNode (all 6 call sites passed true) and stale comments referencing the removed flag.

Why this is the last phase

Drift class	Phase that closed it
Phantom output types (e.g. TSJsxAttributes)	#90 — KnownEstreeType compile-time gate
Shape knowledge duplicated between top-down getters and bottom-up walk	#88, #89 — navigation tables + factory DSL
Synthetic intermediate added without registering in nav tables	this PR — SyntheticLazyNode boundary

After this, every "synthetic intermediate" is grep-able in one place (extends SyntheticLazyNode) and the registration distinction is a class boundary, not a magic constructor arg.

Test plan

• predicate-coverage (152/152 covered, 16 ignored)
• lazy-estree.test (parity sweep + factory tests + phantom-types invariant)
• scope-compat (24/24 fixtures clean)
• selector-analysis, ts-ast-scan, compat-pipeline
• dogfood.js — 107 rules × 30 files, 0 divergences, 0 crashes
• Dify web cold lint — 5.1s on this branch vs 5.1-5.5s on master (no regression)