Fix look_to resulting in NaN rotations

[mockersf]

Objective

• Fixes Camera3dBundle doesn't render anything when looking from above #7802, Fixes NaN when looking_at is called with Transform's origin as target #3736
• Alternative to Add warning about broken rotations to Transform::look_at() docs #6136

Solution

• if direction is parallel to up, use an orthogonal vector
• if direction is zero, use Z

[nicopap]

This is like Elm deciding that 1 / 0 = 0, it might not comply with the purely theoretical definition, but I personally think that functional beats pure. Especially if the selected fallback direction is clearly defined.

[james7132]

I wonder if this means we should be returning Result<Self, SomeError> instead, seems odd to silently fail here.

[alice-i-cecile]

IMO we're not silently failing: we're performing a "best-attempt". I'd be open to try variants too.

[mockersf]

I would prefer to work by default, instead of having to add unwrap / error management everywhere this pops up