Fuzz extensions declarative_net_request::IndexedRule

Implement a fuzzer for covering low-level parsing code in
//extensions/browser/api/declarative_net_request/indexed_rule.cc.

Bug: 1377564
Change-Id: Iae0f9ef15e02635fb23d3fe69555e0279db38420
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3973067


Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1067730}