Research-v13.0.0 anchor.

Includes the following since the previous anchor:

Candidate Tools
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- CWG-F381 "Bugfix for CfL modes with large block sizes”
- CWG-F387 “Training of the context initialization tables”
- CWG-F389 "Fix Coeff Precision after TCQ" (solution 2)
- CWG-F393 “DIP Context Initialization Fix”
- CWG-F400 "BugFix of Warp Modes"
- CWG-F401 "Handling of Refined MV and Reference Padding in Sub-8x8 Chroma"
- Deblock filter sub-PU boundaries for OPFL chroma and for DMVR 16×8 and 8×16 cases
- CWG-F406 "Bug fix for WARP_CAUSAL mode"
- CWG-F426 "Deblocking issues cleanup"
- CWG-F425 "Remove offset-based refinement of intra prediction (ORIP)"
- CWG-F416 "Guided Detail Filter: Gradient Sample Support”
- CWG-F415 "Quantization Matrix Changes"
- CWG-F421 "Intra BAWP condition checks"
- Revert the aspect 4 in F303 for MHCCP division

High-level Syntax
-----------------
- CWG-F233 “Picture struct and Scan type metadata”
- CWG-F255 "Quantization matrix OBU”
- CWG-F153 "Film grain model OBU"
- CWG-F024 “New Key Frame OBUs in AVM”
- CWG-F377 "Sequence Header OBU Changes for reduced_still_picture_header"
- CWG-F356 "Clarification for the show existing frame obu"
- CONFIG_MULTI_LEVEL_SEGMENTATION implementation (Follow-up for CWG-E242)
- Add LCR, Atlas id in the SH and its activation (harmonization of previous proposals)
- CWG-F405 "Removal of Redundant Tile-related Information Signaling in TIP Direct Output Mode”
- CWG-F395 "On the signaling of cross frame CDF initialization"
- CWG-F412 "On sequence header coding tool parameters grouping"
- CWG-F418 "A cleanup of frame level signaling”
- CWG-F419 "On the frame level signaling of the screen content and Intra-BC parameters"
- CWG-F411 "Alpha signalling in the multistream atlas metadata"
- CWG-F417 "More Sequence Header OBU Changes for single_picture_header_flag"
- CWG-F402 "Modifications to the sequence header”
- CWG-F432 "Resolving FGS dependency on CI OBU”
- CWG-F427 "On the signaling of the sequencer header identifier in a bridge frame OBU”
- CWG-F433 "Sequence Header Syntax Reorganization"
- CWG-F430 "On Temporal Point Info Metadata”
- CWG-F322 "Restricted Switch OBU”
- CWG-F270 "Content Interpretation OBU"
- CWG-F446 “Signalling Film Grain Parameters”
- CWG-F436 "Temporal units in AV2" (some parts)

Encoder-only Improvements (Non-normative)
-----------------------------------------
- CWG-F410 “Encoder-only: Transform Partition Search Improvement for Inter Blocks”
- CWG-F383 "Pyramid Quantization Offsets Adjustment for AVM in LD mode"

Encoder / Decoder Speedups (Non-normative)
------------------------------------------
- Add AVX2 for mhccp_predict_hv_hbd()
- Enable row multi-threading by default in decoder
- Enable CDEF and CCSO MT
- Improve and enable Loop restoration frame MT
- Remove redundant memset of mhccp_ref_buf_q3 buffer
- Add frame level lossless check to CDEF and loop filter
- Add AVX2 for mhccp_derive_multi_param_hv()
- Add AVX2 for refinemv_highbd_pad_mc_border for b_w = 11
- Optimize ccso_pre_compute_class_err()
- Optimize AVX2 of av2_highbd_dist_wtd_convolve_2d()
- Optimize av2_opfl_mv_refinement_nxn() for block width 8

Code Cleanups
-------------
- intrapred: remove unused upsample_above/left variables/params
- Unused code cleanup
- CWG-F407 “Code Cleanup: Symbol Renaming in AVM”
- Removal of the compile time flags

Bugfixes
--------
https://gitlab.com/AOMediaCodec/avm/-/milestones/17#tab-issues

High-level Syntax tools NOT included in this anchor (but will be included in next anchor)
-----------------------------------------------------------------------------------------
- CWG-F428 "On level constraints for AV2 specification"
- CWG-F408 "On levels for the AV2 specification" (aspects A, B, F)
- CWG-F431 "HLS changes associated with pictures that are decoded but not used for display"
- CWG-F359 "Buffer handling of frames with Global IBC and In-loop filters enabled”
- CWG-F429 "On maximum layer capacity in OPS, LCR and SH"
- CWG-F436 "Temporal units in AV2"  (some parts)
- CWG-F438 "Remove incomplete metadata types"
- CWG-F414 "On OBU extensibility and trailing bits"
- CWG-F440 "On Decoded Frame Hash Metadata"
- CWG-F441 "Support for higher frame rates in AV2"
- CWG-F447 “Dependency Map Mechanism and Metadata Persistence”
- CWG-F444 “Bug Fix: Modify CICP constraint in the uncompressed header”
- CWG-F449 “FG15 recommendation on the presence of the MSDO, LCR and OPS in different profiles”