[JSC] Optimize Number.prototype.toString on Int32 / Int52 / Double

[JSC] Optimize Number.prototype.toString on Int32 / Int52 / Double
https://bugs.webkit.org/show_bug.cgi?id=167454

Reviewed by Saam Barati.

JSTests:

* stress/number-to-string-abstract-operation.js: Added.
(shouldBe):
(int32ToString):
(shouldBe.int32ToString.new.Number.int52ToString):
(shouldBe.int32ToString.new.Number):
(shouldBe.doubleToString):
* stress/number-to-string-radix.js: Added.
(shouldBe):
(int32ToString):
(shouldBe.int32ToString.new.Number.int52ToString):
(shouldBe.int32ToString.new.Number):
(shouldBe.doubleToString):
* stress/number-to-string.js: Added.
(shouldBe):
(int32ToString):
(shouldBe.int32ToString.new.Number.int52ToString):
(shouldBe.int32ToString.new.Number):
(shouldBe.doubleToString):

Source/JavaScriptCore:

This patch improves Number.toString(radix) performance
by introducing NumberToStringWithRadix DFG node. It directly
calls the operation and it always returns String.

                                               baseline                  patched

    stanford-crypto-sha256-iterative        45.130+-0.928             44.032+-1.184           might be 1.0250x faster

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@214219 268f45cc-cd09-0410-ab3c-d52691b4dbfc