Make findPrototypeId faster

benchmark-findPrototypeId.js

var props = [
  "constructor",
  "toString",
  "toSource",
  "valueOf",
  "charAt",
  "charCodeAt",
  "indexOf",
  "lastIndexOf",
  "split",
  "substring",
  "toLowerCase",
  "toUpperCase",
  "substr",
  "concat",
  "slice",
  "bold",
  "italics",
  "fixed",
  "strike",
  "small",
  "big",
  "blink",
  "sup",
  "sub",
  "fontsize",
  "fontcolor",
  "link",
  "anchor",
  "equals",
  "equalsIgnoreCase",
  "match",
  "search",
  "replace",
  "localeCompare",
  "toLocaleLowerCase",
  "toLocaleUpperCase",
  "trim",
  "trimLeft",
  "trimRight",
  "includes",
  "startsWith",
  "endsWith",
  "normalize",
  "repeat",
  "codePointAt",
  "padStart",
  "padEnd",
  "trimStart",
  "trimEnd",
];

for (var i = 0; i < 1000000; i++) {
  for (var j = 0, len = props.length; j < len; j++) {
    ''[props[j]];
  }
}

/*
$ git checkout improve-findPrototypeId; ./gradlew jar
$ for ((i=0; i<5; i++)); do time java -jar buildGradle/libs/rhino-1.7.14-SNAPSHOT.jar -opt 9 -version 200 benchmark-findPrototypeId.js; done

real	0m5.182s
user	0m5.510s
sys	0m0.329s

real	0m5.395s
user	0m5.605s
sys	0m0.582s

real	0m5.612s
user	0m5.581s
sys	0m0.711s

real	0m5.245s
user	0m5.364s
sys	0m0.556s

real	0m5.105s
user	0m5.171s
sys	0m0.586s


$ git checkout master; ./gradlew jar
$ for ((i=0; i<5; i++)); do time java -jar buildGradle/libs/rhino-1.7.14-SNAPSHOT.jar -opt 9 -version 200 benchmark-findPrototypeId.js; done

real	0m6.088s
user	0m6.184s
sys	0m0.621s

real	0m5.746s
user	0m5.752s
sys	0m0.606s

real	0m5.404s
user	0m5.737s
sys	0m0.297s

real	0m5.508s
user	0m5.743s
sys	0m0.372s

real	0m6.058s
user	0m6.299s
sys	0m0.613s
*/