tp: android.display.video data source, importer, table and stats (#6143)

Adds trace_processor support for the android.display.video data source,
which captures device display frames as a hardware video elementary
stream.

Wire format (protos/perfetto/trace/android/video_frame.proto):
* VideoFrame (TracePacket.video_frame): a codec_config-only frame per
stream (carrying display_name + RFC 6381 codec_string), then one
VideoFrame per on-screen change with a single access unit (au_data).
Self-identifying via a per-session display_id.
* VideoFrameError (TracePacket.video_frame_error): per-stream failure
with a Reason enum (size cap hit, codec error, display gone, no encoder,
display not found, encoder setup failed, virtual display failed).
Config: DataSourceConfig.display_video_config.

Importer (src/trace_processor/plugins/video_frame_importer/):
* Parses video_frame into the __intrinsic_video_frames table. The
encoded payload is stored zero-copy as a TraceBlobView, surfaced via the
__INTRINSIC_VIDEO_FRAME_AU_DATA(id) scalar function (same pattern
HPROF/ETM use for blob payloads).
* Maps each VideoFrameError reason to its own kIndexed entry in the
global stats table, keyed by display_id.
* Enforces a parse-time 256 MB per-stream cap as a backstop against
traces recorded without a producer cap: over-cap frames are dropped and
android_video_size_cap_hit is reported once.

The table is intrinsic (not a stdlib module) since only the VideoFrames
UI consumes it.

Tests: diff tests (single/multi display, au_data blob equivalence, all
VideoFrameError reasons) and a unit test for the parse-time cap.