[ET-VK][conv2d] Re-implement pointwise conv2d with tiled compute and blocked weight packing

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][conv2d_dw] Extract depthwise dispatch into Conv2dDW.cpp with device-based tile selection #18293
• -> [ET-VK][conv2d] Re-implement pointwise conv2d with tiled compute and blocked weight packing #18292
• [ET-VK] Fix staging buffer allocation to check all memory types for HOST_CACHED #18291

Profiling EdgeTAM on Adreno shows pointwise 1×1 convolutions are a dominant
bottleneck. This diff re-implements the stride=1, padding=0 pointwise path
using the same tiled matmul approach as the recently landed linear shader
rewrite.

The new conv2d_pw_tiled shader reuses the shared linear tiled infrastructure
(FPInputTile, FPWeightTile, FPOutTile, fp_accumulate_with_fp_weight, packed
weight tile loading) with custom input/output tile load/store functions that
map flat spatial indices to channels-packed texture3d coordinates.

Weight packing uses the same 4OC×4IC blocked format as linear via the
pack_fp_linear_weight shader. Dispatch uses DynamicDispatchNode for correct
workgroup size updates during graph resizing.

Only the stride=1, padding=0 pointwise path is changed; the general conv2d_pw
shader for arbitrary stride/padding is left unchanged.

EdgeTAM first frame on Samsung S25 (Adreno 830): 208 ms → 196 ms (~6%).

Authored with Claude.

Differential Revision: D96756792

[pytorch-bot]

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❌ 2 New Failures, 2 Unrelated Failures

As of commit db62c0f with merge base ed57040 ():

NEW FAILURES - The following jobs have failed:

• Build Presets / linux (linux, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
  Error response from daemon: Get "https://308535385114.dkr.ecr.us-east-1.amazonaws.com/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t 33d9088e14a8bd420647189f45feb4c46ad7acf3b10071b97ba9cbb15ae89bf4 /exec failed with exit code 139

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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