VDB Merge SOP UI Prototype

[danrbailey]

DRAFT PR - not intended to be merged at this stage.

First attempt to collaborate on designing a SOP UI through code review. This new SOP doesn't depend on the OpenVDB core library or Houdini library so can be built independently (it uses an embedded ds file though I'm not proposing we use this in the final version). No implementation at this stage.

Specifically, I'm looking for any feedback on:

• parameter names and values
• UI layout
• default values
• disablewhen functionality

Not sharing any help documentation in this phase. It's all pretty self-explanatory except for the collation parameter so I'll briefly elaborate with a set of example input VDBs:

1. float "distance" SDF VDB
2. double "distance" SDF VDB
3. float "phi" SDF VDB

Would result in the following:

* Grid Name, Grid Class and Value Type => (1), (2), (3)     // no VDBs merged
* Grid Name and Grid Class => (1) + (2), (3)                // (2) down-sampled to float
* Grid Class and Value Type => (1) + (3), (2)               // "phi" + "distance" merged

[danrbailey]

[danrbailey]

Thank you for providing this. Hopefully these comments make sense!

Great feedback, exactly what I was after, thank you! I'll work on updating with a revised version...

[Idclip]

@danrbailey I realise that #1031 only implemented part of this UI but can this PR now be closed? We can continue to discuss it as a remote branch when work is actioned