Fine. Integrate string table support into binary I/O

Fine-grained manifests previously wrote strings as raw UTF-8, which
increased bytes on the wire and added CPU overhead. This change
integrates string tables into the core BinaryWriter/BinaryReader so
manifests (and other formats) can use string references instead of
duplicated UTF-8 payloads.

What changed
- BinaryWriter
  - Add a shared StringIndexer and expose:
    - writeStringReference / writeStringList /
      writeOptionalStringReference
    - writeStringTableAtEnd() to emit the table and a trailing u32
      offset.
  - Add clone() that shares the StringIndexer with child writers for
    lazy/layered sections.
- BinaryReader
  - Add initializeStringTableAtOffset(offset) (rename from
    createStringTable).
  - Add initializeStringTableFromEnd(), the counterpart to
    writeStringTableAtEnd(), which reads the trailing u32 to find the
    table.
- Bundle writer/reader
  - Switch to writer string-table APIs and use
    initializeStringTableAtOffset() when reading.
  - ResolutionSink now extends BinaryWriter (removes the custom
    _SummaryDataWriter) and AstBinaryWriter delegates string writes to
    the sink.
  - Replace ad-hoc “_writeStringReference/_writeStringList” helpers
    with BinaryWriter methods; move small helpers to extensions.
- Data format
  - Bump AnalysisDriver.DATA_VERSION to 560 to invalidate old caches.

Why
- Reduces duplicate string storage across manifests and resolution
  chunks.
- Lowers serialization cost by replacing repeated UTF-8 blobs with
  compact integer references.
- Unifies string handling across summaries and manifests, simplifying
  future readers/writers.

Trade-offs
- Writers must finalize output correctly (emit the table before
  takeBytes when using the “table at end” mode); misuse will break the
  format.
- Sharing one StringIndexer across cloned writers slightly increases
  table size when many unique strings are produced, but the dedup win
  typically dominates.

Compatibility
- Existing bundle format continues to store four trailing u32 offsets
  (base/resolved/libraries/references/stringTable). The new “table at
  end” read path is added for formats that adopt it; bundle reading
  remains compatible by using the explicit offsets.

Change-Id: I3648a59eeb6af453f2744415c13f864e9b49a167
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/450972
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>

https://dart.googlesource.com/sdk/+/eb938ee4bbca62b27e13859d17b8c0f29c12c9bd