lib: fix two Reflect JSDoc defects - #63740

Two small documentation defects in lib.es2015.reflect.d.ts:

Reflect.set does not document value. The block documents target, propertyKey
and receiver — everything except the value being assigned, which is skipped in the
middle of the list:

/**
 * @param target Object that contains the property on itself or in its prototype chain.
 * @param propertyKey Name of the property.
 * @param receiver The reference to use as the `this` value in the setter function, ...
 */
function set<T extends object, P extends PropertyKey>(
    target: T,
    propertyKey: P,
    value: P extends keyof T ? T[P] : any,   // <- undocumented
    receiver?: any,
): boolean;

Reflect.setPrototypeOf's summary refers to parameters that do not exist. It reads
"Sets the prototype of a specified object o to object proto or null", but the parameters
are named target and proto — there is no o. The wording looks inherited from
Object.setPrototypeOf(o, proto) in lib.es5.d.ts, which does have an o. Renamed the
reference to target and put both parameter names in backticks so they read as
identifiers.

Documentation only; no signatures changed.

Testing

npx hereby runtests-parallel — 106,369 passing, no baseline changes from this PR.
(The full run was done with this change alongside three other lib JSDoc fixes I am
sending separately; the only baselines it moved belong to the [Symbol.matchAll]
parameter rename in that other PR, not to this one.)

Disclosure

This patch was authored with AI assistance (Claude Code). I chose the change, reviewed the
diff, ran the tests locally, and will be the one responding to review feedback.