[Android TRM] Tweak SyncDerivedSuggestionEntrySource for V2 Local Tabs suggestions.

SyncDerivedSuggestionEntrySource (Source) implements common code to
get suggestions from ForeignSessionHelper (V1) and Fetch and Rank
service (V2), handling the need to request data refresh and awaiting
update delay while also triggering update on sync or sign-in status
changes.

Fetch and Rank service recently started to serve Local Tab suggestions.
This causes some mismatch for Source:
* canUseData(): Previously this returns true if and only if user is
  signed in and has enabled sync (Sync Everything). With Local Tabs,
  canUseData() should always return true.
* Caching: This was useful for establishing "fast path" to get data
  quickly and avoid churn (while "slow path" is potentially in flight).
  Local Tab data can change quickly and is easy to retrieve, so now
  "fast path" needs to take this into account.

This CL implements a simple solution to the above: Add new field
|mServesLocalTabs| passed via CTOR.
* For ForeignSessionHelper this is false.
* For Fetch and Rank service this is true. In Source this causes
  canUseData() to true, while also disabling caching. This is important
  for V2 model training, since for this we need to get distinct
  suggestion TrainingIds on each read for RecordAction().

Additional changes:
* SuggestionBackend: Rename readCached() to read(). Propagate the name
  change, and update comments re. "cached".
* TabResumptionModuleEnablement.SyncDerived:
  * Add isV2Enabled() and isV2EnabledWithLocalTabs().
  * Fix shouldMakeProvider() to account for the case where sign-in /
    sync is disabled, but V2 Local Tab suggestions still possible.

Tests:
* SyncDerivedSuggestionEntrySourceTest: Add 2 tests to contrast the
  effects of passing false or true to |mServesLocalTabs|.

Bug: 344949868, 343209609
Change-Id: Ia90413dab9a8d7e6e74622469815c27c12c9b798
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5598571


Commit-Queue: Samuel Huang <huangs@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Xi Han <hanxi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1311059}