ggml webgpu: support for backend sampling (#18880)
* ggml webgpu: add SOFTPLUS unary operator
Implements SOFTPLUS (log(1 + exp(x))) with f16/f32 support. Uses f32
precision for intermediate calculations to prevent f16 overflow.
* Add shader implementation and 4 variants (f32/f16, inplace/non-inplace)
* Register pipelines and device support
* Follow Vulkan backend numerical stability pattern
* ggml webgpu: add EXPM1 unary operator
Implements EXPM1 (exp(x) - 1) with f16/f32 support.
* Add shader implementation and 4 variants (f32/f16, inplace/non-inplace)
* Register pipelines and device support
* ggml webgpu: add FLOOR unary operator
Implements FLOOR (rounds down to nearest integer) with f16/f32 support.
* Add shader implementation and 4 variants (f32/f16, inplace/non-inplace)
* Register pipelines and device support
* ggml webgpu: add CEIL unary operator
Implements CEIL (rounds up to nearest integer) with f16/f32 support.
* Add shader implementation and 4 variants (f32/f16, inplace/non-inplace)
* Register pipelines and device support
* ggml webgpu: add ROUND unary operator
Implements ROUND (rounds to nearest integer) with f16/f32 support.
* Add shader implementation and 4 variants (f32/f16, inplace/non-inplace)
* Register pipelines and device support
* ggml webgpu: add TRUNC unary operator
Implements TRUNC (truncates towards zero) with f16/f32 support.
* Add shader implementation and 4 variants (f32/f16, inplace/non-inplace)
* Register pipelines and device support
* docs : update WebGPU support for unary operators (FLOOR, CEIL, ROUND, TRUNC, EXPM1, SOFTPLUS)
* Updates to webgpu get_memory
* Add argmax
* Add argmax,cumsum,sum,sum_rows
* Add necessary CPY/GET_ROWS operators
* Support for argsort using multi-pass strategy
* Update set_rows for i32 indices, move to pre-wgsl
* Port unary operators to pre-wgsl and support FILL
* Implement PAD
* Add support for top-k
* clean up, scope pipeline init mutex
* fix newline
* Add support for log
* Update LOG for better precision, and ops doc
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Co-authored-by: Abhijit Ramesh <abhijitramesh2k@gmail.com>
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