Switch Excel support to XLSX.jl

[TimG1964]

I will need to make a new release of XLSX.jl for this, but would prefer to know the version of FileIO.jl needed for compats. XLSX.jl is ready to go - you can inspect it here if you wish.

Will resolve #428.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.09%. Comparing base (3c40adc) to head (72d5be7).

Files with missing lines	Patch %	Lines
src/registry.jl	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #439      +/-   ##
==========================================
- Coverage   91.17%   91.09%   -0.08%     
==========================================
  Files          11       11              
  Lines         714      719       +5     
==========================================
+ Hits          651      655       +4     
- Misses         63       64       +1     

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[TimG1964]

Had to add magic bytes as well as extensions to get over ambiguity with NPZ.

[TimG1964]

As with #124, "There is a bit of a chicken and egg situation here": the tests in XLSX.jl can only pass once this here is merged and tagged, but this here obviously only works if the extension to XLSX.jl is merged and tagged.

I've put the XLSX.jl tests inside a version check on FileIO.jl, but it would be good to know which tagged version of FileIO.jl is (or will be) the first that supports XLSX.jl. I can then tag a new release.

[SimonDanisch]

Yeah, I also haven't found a patented solution for this...
You could manually depend on this branch in CI while its not tagged, or manually register in init or in the tests...
I guess the best solution would be to only change test code and not have it in init or so, so that the switch can be done cleanly.

[TimG1964]

I've tested on my own fork, so I know tests pass. I just don't want to tag a release until I know what version of FileIO will eventually work.

In my runtests.jl file, I have

if Pkg.pkgversion(FileIO) > v"1.19.0"
    @testset "FileIO" verbose=true begin
            # do the tests
    end
else
    @info "Skipping FileIO tests (requires FileIO > v1.19.0, got $(pkgversion(FileIO)))"
end

So it is just a question of knowing the version to use in the condition. I can tag a release as soon as I know this for certain.