vulkan: use fp32 in coopmat2 q4_k dequant function

[jeffbolznv]

This is stacked on #12273 and uses fp32 in dequantFuncQ4_K. It's kind of a toss up whether fp16 of fp32 will be faster, and this was the only function I found where it's currently faster.

Results for Phi-3-mini-4k-instruct-q4.gguf on RTX 4070:

		PR12273		this PR		speedup
					
        pp5	466.92		463.51		-0.73%
       pp10	517.04		561.56		8.61%
       pp20	1045.43		1105.62		5.76%
       pp31	1730.83		1664.51		-3.83%
       pp32	1745.39		1837.95		5.30%
       pp33	1512.23		1472.52		-2.63%
       pp48	2249.4		2136.36		-5.03%
       pp54	2318.44		2398.81		3.47%
       pp63	2694.4		2733.02		1.43%
       pp64	2764.43		2725.61		-1.40%
       pp65	2260.9		2326.46		2.90%
       pp80	2835.27		2836.59		0.05%
       pp96	3189.51		3229.14		1.24%
      pp112	3632.44		3722.96		2.49%
      pp113	3656.96		3736.39		2.17%
      pp127	4087.5		4207.86		2.94%
      pp128	4174.96		4269.83		2.27%
      pp129	2734.41		2848.4		4.17%
      pp140	2907.37		3102.99		6.73%
      pp160	3356.15		3497.35		4.21%
      pp180	3639.65		3913.92		7.54%
      pp192	3857.68		4178.85		8.33%
      pp200	3979.56		4301.45		8.09%
      pp210	4258.49		4393.56		3.17%
      pp230	4589.22		4693.42		2.27%
      pp248	4761.21		5352.42		12.42%
      pp255	5024.18		5221.56		3.93%
      pp256	4919.83		5210.66		5.91%
      pp257	3788.88		3894.24		2.78%
      pp280	4150.83		4192.77		1.01%
      pp300	4432.56		4462.49		0.68%
      pp320	4545.71		4779.86		5.15%
      pp350	4877.21		5035.38		3.24%
      pp384	5189.39		5423.55		4.51%
      pp410	4580.83		4722.13		3.08%
      pp448	4945.34		5059.5		2.31%
      pp480	5208.15		5248.98		0.78%
      pp490	5185.52		5370.3		3.56%
      pp511	5365		5572.95		3.88%
      pp512	5398.73		5547.35		2.75%
      pp513	4958.86		5081.44		2.47%
      pp767	5141.08		5422.29		5.47%
      pp768	5175.3		5299.44		2.40%
      pp769	4685.68		4780.83		2.03%
     pp1023	5300.75		5482.69		3.43%
     pp1024	5294.66		5537.79		4.59%
     pp1025	5023.31		5230.2		4.12%
     pp2047	5117.1		5308.24		3.74%
     pp2048	5116.32		5272.6		3.05%
     pp2049	5016.38		5123.08		2.13%