Update to stb_image version 2.29 for stbi_info() fix

[angusdavisadobe]

Description of Change(s)

Update to the latest version of stb_image

Fixes Issue(s)

There was a bug fix to stb_image where previously, stbi_info() (and sbti_info_from_memory()) would return the wrong value for nchannels for a grey scale png image with an alpha channel. For a particular png, stbi_info() would incorrectly return 1 but when later calling stbi_load() with a pre-allocated block of memory to fill, the load method would detect that there are two channels and would overflow memory when decoding, causing a crash in hydra.

The changes are to update to version 2.29 of stb_image and make the appropriate updates to pxr/image/hio/stbImage.cpp to account for api changes to the stb_image_resize functions.

• 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-9107

[tcauchois]

Hi Angus,

This PR isn't building for us; we get an array overrun in stb_image_resize2.h, that's statically detectable by the compiler. Would you be able to update the PR so it builds?

Thanks!
Tom