[C++] Remove superfluous static constexpr definitions

[pitrou]

Since C++17, static constexpr members are automatically considered inline.

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[github-actions]

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[pitrou]

This will probably fail on MinGW (as fixed elsewhere by 3ec3939), but let's try anyway. @felipecrv

[pitrou]

Weirdly, MinGW seems to pass, but we should try again after #42236 is merged (perhaps a type_id member reference in a test makes it fail?).

[pitrou]

I rebased with #42236 now merged, let's see what entails.

[pitrou]

... and indeed MINGW fails.

[pitrou]

Ok, it seems that even an explicit inline qualifier doesn't help. This seems to be a bug in the MINGW64 port of gcc, so we'll have to live with it until we upgrade or demote that compiler in CI. @kou

[pitrou]

For reference, the linker error:

D:/a/_temp/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: src/arrow/compute/kernels/CMakeFiles/arrow-compute-vector-test.dir/vector_nested_test.cc.obj:vector_nested_test.cc:(.text$_ZN5arrow7compute12SwapListViewINS_12ListViewTypeEiEEvPNS_9ArrayDataExx[_ZN5arrow7compute12SwapListViewINS_12ListViewTypeEiEEvPNS_9ArrayDataExx]+0x117): undefined reference to `__imp__ZN5arrow12ListViewType7type_idE'
D:/a/_temp/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: src/arrow/compute/kernels/CMakeFiles/arrow-compute-vector-test.dir/vector_nested_test.cc.obj:vector_nested_test.cc:(.text$_ZN5arrow7compute11SetListViewINS_12ListViewTypeEiEEvPNS_9ArrayDataExT0_S5_[_ZN5arrow7compute11SetListViewINS_12ListViewTypeEiEEvPNS_9ArrayDataExT0_S5_]+0x12f): undefined reference to `__imp__ZN5arrow12ListViewType7type_idE'

Some special handling is probably required for static inline members of dllexport classes. CLang handles them properly, but gcc doesn't, apparently.