This changes the Name::hash_field and Symbol::flags to uint32_t as
well, so that both Symbols and Strings consume one fewer word on 64-bit
architectures now. More importantly the access to String::length is
always a 32-bit field load now, even with 31-bit Smis (i.e. on ARM or
on 64-bit with pointer compression), so the access should be faster.

Bug: v8:7065, v8:8171
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng;luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I5523deb1f84ece91fa2fea775d50318bd1300493
Reviewed-on: https://chromium-review.googlesource.com/1221288
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55825}