Add antsApplyTransformsToTRX

[mattcieslak]

Closes #1947

Description

This PR adds a command line executable antsApplyTransformsToTRX, which can apply ITK warps to streamline coordinates. This replaces a workflow that was similar to GIFTI, where we used to convert the coordinates to a csv and use antsApplyTransformsToPoints.

The ITK remote module buffers the coordinates so this ends up requiring very little memory, even with gigantic streamline datasets.

The TractographyTRX remote module needs an update to build with the most recent 6.0 beta, but the rest of this code is ready for review!

[cookpa]

Thanks for this, are we waiting for the merge of InsightSoftwareConsortium/ITK#5955 ?

[mattcieslak]

yes, and I was also wondering if you think it would be helpful to add TRX support anywhere else. I was thinking maybe adding trx support to PrintHeader so it can list all the metadata fields or something like that. It could be useful for testing that the metadata is carried forward into the resampled TRX

[cookpa]

That's an interesting idea, PrintHeader is specialized for image data and it might be best to keep that interface as-is, since it's pretty widely used. It would be nice to have a related program that can handle "unstructured points" like GIFTI, TRX, etc.

[cookpa]

@mattcieslak is this ready to merge?

[mattcieslak]

Yep, this is good to go!

[cookpa]

Thanks very much. I will merge now but might edit some things before we make a release based on this