[zip] Add ZipReader::Entry

Preparing the transition from (class) ZipReader::EntryInfo to (struct)
ZipReader::Entry. This will remove boilerplate code, and will provide
optimization and simplification opportunities.

Avoid dynamically allocating the Entry over and over again. Reuse the
same internal Entry object.

BUG=chromium:1295127
TEST=autoninja -C out/Default zlib_unittests && out/Default/zlib_unittests

Change-Id: Ie51e1bda05408b28f53957ea89c78d37d8009f5c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3446405


Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: François Degros <fdegros@chromium.org>
Cr-Commit-Position: refs/heads/main@{#968767}
NOKEYCHECK=True
GitOrigin-RevId: 153ddbabb7339501c16310337d9b240c37929fb6