Add utilites 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.

• [X] I have verified that all unit tests pass with the proposed changes
• [X] I have submitted a signed Contributor License Agreement

[jesschimein]

Filed as internal issue #USD-9596

[jesschimein]

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