add opencl support

[VarLad]

imports and re-exports OpenCL from MLDataDevices, for usage in Flux.jl
Depends on LuxDL/Lux.jl#1590

[VarLad]

Marking as draft until the MLDataDevices PR is merged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.93%. Comparing base (64c3979) to head (5af3c22).

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #2635       +/-   ##
===========================================
+ Coverage   32.09%   65.93%   +33.84%     
===========================================
  Files          32       33        +1     
  Lines        2038     2087       +49     
===========================================
+ Hits          654     1376      +722     
+ Misses       1384      711      -673     

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[VarLad]

@CarloLucibello Should I bump the minimum required version of MLDataDevices as well?

[CarloLucibello]

Should I bump the minimum required version of MLDataDevices as well?

yes.

Can we add some tests, e.g. for Dense forward and backward passes?

[VarLad]

@CarloLucibello will these be good enough?
I'm not sure how to enable them in CI though 😓
But no special machine should be required, since its using the CPU backend (provided as a jll) in the tests.