Rework strtod and parseFloat (#768)

Also fixes an issue with String.fromCodePoint and improves strtol

Author: MaxGraey

Diff for: std/assembly/index.d.ts

@@ -1501,6 +1501,8 @@ interface INativeMath<T> extends IMath<T> {
   sincos_cos: T;
   /** Seeds the random number generator. */
   seedRandom(value: i64): void;
+  /** Multiplies a floating point `x` by 2 raised to power exp `n`. */
+  scalbn(x: T, n: i32): T;
   /** Returns the floating-point remainder of `x / y` (rounded towards zero). */
   mod(x: T, y: T): T;
   /** Returns the floating-point remainder of `x / y` (rounded to nearest). */

Diff for: std/assembly/string.ts

@@ -26,9 +26,9 @@ import { idof } from "./builtins";
       store<u16>(out, <u16>code);
     } else {
       code -= 0x10000;
-      let hi: u32 = (code >>> 10) + 0xD800;
       let lo: u32 = (code & 0x3FF) + 0xDC00;
-      store<u32>(out, (hi << 16) | lo);
+      let hi: u32 = (code >>> 10) + 0xD800;
+      store<u32>(out, hi | (lo << 16));
     }
     return changetype<string>(out); // retains
   }