Add utilities for processing ies light files

[pmolodo]

Description of Change(s)

This adds ies.h and ies.cpp, for processing ies light files.

These are originally taken from blender, v4.1.1:

• https://github.com/blender/blender/blob/v4.1.1/intern/cycles/util/ies.h
• https://github.com/blender/blender/blob/v4.1.1/intern/cycles/util/ies.cpp

These files are provided by Blender under the Apache 2.0 license. (See the note here about how the "Blender Cycles rendering engine is available as Apache 2.0").

These are not yet built / used, but merely introduce the files for use in the codebase later (ie, as part of a reworked UsdLux update).

The intent is to allow the Pixar legal approval process to get started early.

• I have verified that all unit tests pass with the proposed changes

• I have submitted a signed Contributor License Agreement

[jesschimein]

Filed as internal issue #USD-9596

[jesschimein]

/AzurePipelines run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pmolodo]

Updated the way that these files are vendored, to match how pxrCLI11 works - ie, with a patch file.

[jesschimein]

/AzurePipelines run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pmolodo]

This PR doesn't actually build/use ies.h or ies.cpp yet, as we don't want to slow down / alter the actual build until this code is used - this is to get the legal process started - but look at this pr/ies_build branch for one that will build ies.cpp, to validate it at least compiles:

https://github.com/pmolodo/OpenUSD/commits/pr/ies_build/

[jesschimein]

/AzurePipelines run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[pmolodo]

If it helps to get approval from legal - I've since learned that the exact same source code is also hosted in a separate "cycles" repository. The two files in question are the exact same (which I confirmed), and both explicitly say in their headers that they're covered by Apache 2.0:

* SPDX-License-Identifier: Apache-2.0 */

However, the cycles repo has the additional nice feature that the license listed at the root of the project is the Apache 2.0 one.
I can update this PR to reference the cycles repo, instead of the blender one, if it would be preferrable.

Relevant Links:

• Repo: https://projects.blender.org/blender/cycles/
• v4.1.1: https://projects.blender.org/blender/cycles/src/tag/v4.1.1
• ies.h: https://projects.blender.org/blender/cycles/src/tag/v4.1.1/src/util/ies.h
• ies.cpp: https://projects.blender.org/blender/cycles/src/tag/v4.1.1/src/util/ies.cpp
• LICENSE: https://projects.blender.org/blender/cycles/src/branch/main/LICENSE

[pmolodo]

Closing in favor of:

• [hdEmbree] Add utilities for processing ies light files (hdEmbree-UsdLux-PR15) #3192