[builtins] Re-enable Map and WeakMap constructor fast path.

If an entry may have side effects (non-fast JS Array), restart and add all entries in slow path.

- Move allocating and setting table into AddConstructorEntries.
- Move handling non-object map entries into LoadKeyValue.
- AddConstructorEntry and LoadKeyValue go to a label when adding a map entry may have side effects.

Bug: chromium:798026, chromium:799364
Change-Id: I3c28594fc4a8379a106413e19e6df9e83eeb5278
Reviewed-on: https://chromium-review.googlesource.com/874786Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Peter Wong <peter.wm.wong@gmail.com>
Cr-Commit-Position: refs/heads/master@{#50729}