refactor: retire function-keyword in favor of arrow/method syntax (reconstruct #474 on current master) - #589

Summary

Reconstructs endojs/endo-but-for-bots#474
(refactor: retire function-keyword in favor of arrow/method syntax per erights review, merged)
on the current upstream endojs/endo master, rather than cherry-picking #474's commits onto a
stale base.

Per erights's review, function-keyword functions carry four hazards inside hardened-JavaScript code
(they have [[Construct]], an irrelevant prototype, freeze ≠ harden, and declaration hoisting/TDZ
hazards). Arrow functions and concise methods have none of these and are the desired default. This PR
converts function-keyword declarations/expressions to arrow / concise-method syntax across the same
package set #474 covered, keeps the documented legitimate exceptions, and (re)establishes the house-style
convention doc.

How this differs from the merged #474

• Re-applied to the current tree, not cherry-picked. The base here is the current upstream master
  snapshot (master-0594e99). The transformation was re-derived against that tree; where a conversion had
  already been absorbed upstream (e.g. pass-style/src/byteArray.js, passStyleOf.js), the net change is
  zero and the file simply does not appear in this PR.
• Same scope as refactor: retire function-keyword in favor of arrow/method syntax per erights review #474. 17 packages, ~93 sites, plus the follow-up refinements that landed on refactor: retire function-keyword in favor of arrow/method syntax per erights review #474's
  branch (BaseHandledPromise rename, concise generator methods in captp/daemon, the init
  AsyncLocalStorage descriptor-form install, and the cross-reference notes at exception sites).
• House-style doc. docs/house-style/function-keyword.md is present and current (rationale, conversion
  rules, and the full legitimate-exception list), linked from AGENTS.md.

Legitimate exceptions kept (unchanged from #474)

Constructor emulation (BaseHandledPromise, NewCompartment, SES inert constructors, ModuleSource/
AbstractModuleSource), standalone generator/async-generator expressions and intrinsic-prototype
sentinels (trampoline, ses/commons.js, compartment-mapper, daemon), vendored/third-party code
(cjs-module-analyzer, test262), the sloppy-mode getThis probe, TS-assertion-via-arrow+@overload,
and module-init forward references (convertValToSlot/convertSlotToVal, serializeAndSendMessage,
safeRequire). See the house-style doc for the full rationale.

Out of scope (follow-up)

An audit of the current tree surfaced further un-migrated function-keyword sites in SES files that
#474 never touched — the lockdown/taming dispatch functions (tame-*.js), permits-intrinsics.js,
permits.js, enable-property-overrides.js, make-evaluate.js, and SES's own make-hardener.js. These
are outside #474's original scope and several sit on the security-critical SES initialization boundary, so
they are deliberately left for a separate, individually-reviewed pass rather than folded into this
reconstruction.

Verification

• eslint on all changed files: 0 errors (4 pre-existing-style jsdoc/require-param warnings on the
  converted daemon generator methods, identical to refactor: retire function-keyword in favor of arrow/method syntax per erights review #474's merged form; non-fatal).
• node --check on every changed file: clean.
• Package test spot-checks (zip, trampoline, eventual-send): green. The conversion preserves arity,
  return value, and this binding — the intended behavioral diff is zero.
• Full build/tsc/test runs via CI.

Upstream counterpart

The canonical upstream PR for this work is endojs/endo#3312
(refactor: retire function-keyword in favor of arrow/method syntax, OPEN). This fork PR mirrors #3312's
transformation; the head tree here is identical to #3312's, rebased onto a fresh frozen base
(master-2708cac, a snapshot of the current upstream endojs/endo master). The earlier boatman-created
duplicate #3318 is closed and is not tracked.