iModel transformations do not remap/preserve texture references.

[MichaelBelousov]

Describe the bug iModel transformations do not remap/preserve texture references.

To Reproduce Create an iModel with some geometry that contains a texture, and use the imodel-transformer test app to identity-transform it into a new file, textures will be gone if you open it in a viewer. This applies to normal maps, patterns, diffuse textures (see below for a more specific repro).

Expected behavior Textures are preserved in an identity transformation.

Desktop (please complete the applicable information):

• OS: All
• Browser: N/A
• Version: All
• iTwin.js Version: all known versions

[pmconne]

More specifically (correct me if you disagree @MichaelBelousov):

• Create a RenderMaterialElement containing a pattern map and/or normal map
• (Optionally, apply it to a geometric element and verify the pattern/normal map are applied at display time)
• Perform a transformation that preserves the material.
• Expect: the pattern/normal map texture elements should have been copied. The material's references to their Ids in its JSON properties should have been remapped. If the material was applied to a geometric element, the maps should still apply at display time.

RenderingAsset::Relocate looks completely broken.