Move SetSerializedCachedMetadata into CachedMetadataHandler

ScriptCachedMetadataHandler::SetSerializedCachedMetadata() was
introduced to allow cached metadata, persisted by the platform, to
be proactively set on the handler for consumption during V8
script compilation.

This method is different to SetCachedMetadata(), which is called
by blink following resource compilation in v8, and asks the
platform to persist this data after the fact.

This CL updates the method comments to better clarify this
distinction and moves the method into the CachedMetadataHandler base
class. This enables all CachedMetadataHandlers to receive data from
the embedding platform and simplifies handler extension.

Downstream code will leverage this to support a handler for code
cache metadata served from chrome's static resource bundle (see
linked bug for context).

Bug: 378504631
Change-Id: I64a18909b34448cbfe67c32c7413b5ca3410ec7d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6171641
Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1415098}