Port 322ffda3

Original commit message:
    Also migrate the Number constructor to a native builtin, using the
    same mechanism already used by the String constructor. Otherwise just
    parsing and compiling the Number constructor to optimized code already
    eats 2ms on desktop for no good reason, and the resulting optimized
    code is not even close to awesome.

    Drive-by-fix: Use correct context for the [[Construct]] case of the
    String constructor as well, and share some code with it.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1583903002

Cr-Commit-Position: refs/heads/master@{#33272}