[glTF] Scenes with a camera are not rendered correctly

[footballhead]

Some examples:

• Duck is mostly off-screen

Expected	Actual

• EnvironmentTest doesn't show anything:

Expected	Actual

• IridescentDishWithOlives is stretched. Subsections of 3.10.3 say that

When the provided camera’s aspect ratio does not match the aspect ratio of the viewport, client implementations SHOULD NOT crop or perform non-uniform scaling (“stretching”) to fill the viewport.

Expected	Actual

• ToyCar is also similarly stretched