improve webidl.is.x performance for common case

[KhafraDev]

The trade off is although the more common case is 40x faster, the bad case is much slower.

ie. FormData.prototype.append.call({}, ...) will be ~7x slower than before.

cpu: Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
runtime: node v22.9.0 (x64-win32)

benchmark                                time (avg)             (min … max)       p75       p99      p999
--------------------------------------------------------------------------- -----------------------------
common (good) case - isPrototypeOf     3.42 ns/iter    (3.22 ns … 54.74 ns)   3.37 ns   5.47 ns  10.01 ns
uncommon (bad) case - isPrototypeOf    4.46 ns/iter     (4.3 ns … 46.34 ns)   4.35 ns   6.69 ns  11.77 ns
common (good) case - #symbol in fd       87 ps/iter        (49 ps … 211 ns)     98 ps     98 ps    391 ps !
uncommon (bad) case - #symbol in fd   28.11 ns/iter   (27.59 ns … 69.63 ns)  27.93 ns  33.25 ns  48.19 ns

summary
  common (good) case - #symbol in fd
   39.14x faster than common (good) case - isPrototypeOf
   51.01x faster than uncommon (bad) case - isPrototypeOf
   321.47x faster than uncommon (bad) case - #symbol in fd