[ExecuTorch][WebGPU] Test coverage for the f16-accumulate steel GEMM #10262

Job	Run time
test-arm / test-backend-linux (arm_tosa_fp, operators) / linux-job	16m 7s
test-arm / test-backend-linux (arm_vgf_fp, models) / linux-job	16m 31s
test-arm / test-backend-linux (arm_tosa_fp, models) / linux-job	16m 35s
test-arm / test-backend-linux (arm_vgf_fp, operators) / linux-job	17m 54s
test-arm / test-backend-macos	-8s
test-arm / package-golden-artifacts	43s
	1h 7m 42s

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