This reverts commit 42667bab.

Reason for revert: Breaks msvc compile:
https://build.chromium.org/p/client.v8/builders/V8%20Win64%20-%20msvc/builds/908

Original change's description:
> Simplify FunctionKind, saving 4 bits in SharedFunctionInfo
> 
> Since we only need to store 18 different function kinds,
> the bitfield approach was wasting space (requiring 11 bits).
> 
> This patch replaces the bitfield with a regular enum, and
> updates all the FunctionKind predicates to use comparisons
> instead of bitwise ops.
> 
> For the small amount of builtin code that depended upon being
> able to do masking to determine whether something is a class
> constructor, we still store two extra bits on FunctionKind,
> which are computed when the SFI is initialized.
> 
> If this approach causes performance regressions (i.e., if it
> turns out that other code was implicitly depending on masking
> for fast checks), we can revert this or address it in
> other ways (e.g., by doing similar caching of repeated checks
> in the caller).
> 
> Change-Id: Iebb3214f564ea8bd7b21e78fda33517d63247124
> Reviewed-on: https://chromium-review.googlesource.com/860896
> Commit-Queue: Adam Klein <adamk@chromium.org>
> Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50559}

TBR=adamk@chromium.org,gsathya@chromium.org

Change-Id: I8e1faa0ca6213d1e70a00fcb417b1bfa35ebd643
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/866310Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50561}