`span`-ify around `components/subresource_filter/.../indexed_ruleset.cc`

This CL starts by tweaking the `LocalGetChecksum` function in
`components/subresource_filter/core/common/indexed_ruleset.cc` to accept
a `base::span<const uint8_t>` parameter instead of a pointer+size pair.
This change is motivated by the desire to `span`-ify the
`base::PersistentHash` function (i.e. to eventually remove the overload
taking pointer+size pair).

The remainder of the CL makes additional follow-up changes needed to
ensure that the code still compiles (i.e. we need to use `base::span` in
a few other places).

This CL is meant to have no impact on behavior.  And therefore there
should be no need to update `RulesetIndexer::kIndexedFormatVersion`.

Change-Id: Ie6fa3d13a09412e33941d0f1fba6452924909c9b
Bug: 1490484
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5207255
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1250508}