{StaticCharVector}, according to its name, should return a
{Vector<const char>}. For getting a {Vector<const uint8_t>}, the method
should be called {StaticOneByteVector}, analog to the
{OneByteVector} methods that already exist.

Also, {StaticCharVector} is constexpr, but {StaticOneByteVector} cannot
be, since it contains a {reinterpret_cast}. The same holds for
{Vector::cast} in general.

This CL
- changes the return type of {StaticCharVector} to be
  {Vector<const char>},
- introduces a new {StaticOneByteVector} which returns
  {Vector<const uint8_t>},
- fixes constexpr annotations at various methods returning {Vector}s,
- refactors users of {StaticCharVector} to either use
  {StaticOneByteVector} instead, or work on {char} if that makes more
  sense.

R=leszeks@chromium.org

Bug: v8:10426
Change-Id: I71e336097e41ad30f982aa6344ca3d67b3a01fe3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2154196
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67213}