[USDU-230][USDU-232][USDU-275] Add testcases regarding texture mapping

[lee-aandrew]

Purpose of this PR

Ticket/Jira #:
[USDU-230][USDU-232][USDU-275]

Testing

Functional Testing status:

Adds Testcases:

• ImportAsPrefab_TextureDataImported: Tests if Import as Prefab functionality keeps texture data set in USDA file
• ImportAsGameObjects_TextureDataImported: Tests if Import as GameObject functionality keeps texture data set in USDA file
• ImportAsGameObject_TextureDataImported_FromUsdz: Tests if Import as GameObject from USDZ file keeps texture data set in original USDA file

Overall Product Risks

ImportHelper.cs:

• Added another ImportAsPrefab that takes in a SceneImportOptions
• GetSelectedAssetPath: private -> public (needed access from a test script)
• GetDefaultRoot: private -> public (needed access from a test script)

Complexity:
1

Halo Effect:
1

Additional information

Note to reviewers:

Reminder:
Requires: #327 to be pushed in first

[vickycl]

Can we reduce the sizes or remove some of the textures please? A few 100kb can add up quite quickly over the amount of times they're downloaded, and they could be really tiny and still function the same in these tests.

[vickycl]

Very nice! Just a few small requests:

• Textures could still be smaller :P a single texture of a single colour shouldn't need to be more than 64x64pix, maybe even less.

• I don't see a test in here for USDU-275 (which I don't think has been fixed, so would fail anyway), am I missing something?

[vickycl]

Looks good! Thank you for the iterations :)

[lee-aandrew]

Thank you for the reviews @vickycl and @unity-chris !