Refactor Proxy trap dispatch into a shared skeleton with lazy argument construction

[lahma]

Restructures JsProxy so all 13 internal methods follow one uniform shape:

var trap = GetTrap(TrapX);          // revocation check + spec GetMethod, fetched fresh per op
var target = _target;               // [[ProxyTarget]] captured once, per spec
if (trap is null)
{
    return target.X(...);           // absent trap forwards, allocation-free
}
var result = CallTrap(trap, ...);   // arguments built only on this path
ValidateXTrapResult(target, ...);   // invariant checks, logic unchanged, handler-agnostic

What this buys:

• Trap-less forwarding no longer allocates. Argument arrays, the apply/construct CreateArrayFromList array, and the defineProperty descriptor object were built before discovering the handler lacks the trap. The spec orders trap fetch before argument materialization, so building lazily is unobservable.
• Spec fix — revoke-during-trap crash. The invariant validators used to re-read _target after the trap returned, so a trap revoking its own proxy (r.revoke() inside a set/deleteProperty/has trap) hit a NullReferenceException. Per spec, [[ProxyTarget]] is read once at the top of each internal method; validators now receive the captured target. Node 24/V8-verified regression tests added.
• Message alignment: the revoked [[Get]] error now says Cannot perform 'get' on a proxy... (trap name) instead of the property name — character-identical to V8.
• The invariant blocks live in Validate*TrapResult methods so trap acquisition and validation are visibly separated. This is also groundwork for a follow-up that lets CLR code implement traps directly (ProxyHandler), which will branch inside the same funnel and reuse the same validators.

Verification: full test262 suite 99,429 passed / 0 failed; ProxyTests 43/43 (3 new revoke-during-trap tests); full Jint.Tests + Jint.Tests.PublicInterface green.

ProxyBenchmark (#2666) before/after, DefaultJob:

Lane	Time	Allocated
ForwardGet	−4.3%	4,689 KB → 1.3 KB
ForwardSet	−27.4%	45,775 KB → 5,931 KB
ApplyForward	−30.5%	25,143 KB → 5,611 KB
TrapSet	−16.5%	flat
ConstructTrap	−12.7%	flat
TrapGet / TrapHas / OwnKeys* / ApplyTrap	−2..−7%	flat or lower
RevocableCreate / RevokedTypeof	flat (multi-launch verified)	flat

🤖 Generated with Claude Code

https://claude.ai/code/session_01EsHuKuE4UihKZp5HYapDHE