Swap dimensions of some direct transform work arrays

[samhatfield]

This is to avoid implicit transpositions and associated unnecessary memory copies.

Work carried out by Dmitry Pekurovsky dpekurovsky@nvidia.com.

Note: this PR came out of a collaboration between ECMWF and Nvidia. We hope to have it merged at some point, but until then I'll leave it as a draft PR.

TODO:

• Instead of using EXEC_EFFTW, redefine EXEC_FFTW. EXEC_EFFTW should technically only be used for the limited area version of ecTrans, etrans. @dmitrypek only used this because it happened to already have the correct array dimension ordering.
• Implement a similar modification of the inverse transform.
• Fix FLT implementation so all tests pass.

[samhatfield]

I'm going to close this for now as significant work would be required to get this into a PR-able state. I may revisit it in future.