InteractableRotationTheme is using world rotation as start value

[BertrandOustriere]

Describe the bug

InteractableRotationTheme is using a world rotation for the interpolation's start value :

/// <inheritdoc />
public override ThemePropertyValue GetProperty(ThemeStateProperty property)
{
    ThemePropertyValue start = new ThemePropertyValue();
    start.Vector3 = hostTransform.eulerAngles;
    return start;
}

/// <inheritdoc />
public override void SetValue(ThemeStateProperty property, int index, float percentage)
{
    Vector3 lerpTarget = property.Values[index].Vector3;

    bool relative = Properties[0].Value.Bool;
    if (relative)
    {
        lerpTarget = originalRotation + lerpTarget;
    }

    hostTransform.localRotation = Quaternion.Euler(Vector3.Lerp(property.StartValue.Vector3, lerpTarget, percentage));
}

Since the interpolation is setting the local rotation in the SetValue function, this induces weird behaviour in some cases, for exemple when the parent transform of the rotated object has a rotation different from Vector3.zero

By using hostTransform.localEulerAngles in the GetProperty function, the issue seems to be fixed.

To reproduce

Steps to reproduce the behavior:

1. Open the InteractableExamples scene
2. Set a random rotation to the object Model_Bucky (for example I used 12,80,67)
3. Press play and hover the object with your cursor to reach the focus state.

Your setup (please complete the following information)

• Unity Version 2019.2.6f1
• MRTK Version 2.2

Target platform (please complete the following information)

• HoloLens
• HoloLens 2

[wiwei]

Side note: I updated the PR description text and replaced hostTransform.localEulerAngles with hostTransform.eulerAngles, because I'm assuming that the text was intended to show the code as-is (with the issue that exists today), not the fix that was proposed.

[wiwei]

@thalbern it seems like this is actually just a bug due to the non-mirrored nature of the set/get (i.e. non local in one, local in the other) - it seems like making them be mirrored would be the right thing to do, but I guess it might also be a question of which one is the more 'correct' one. Do you have any background/thoughts on this one?

Otherwise there might be some compat concerns (i.e. people now taking a dependency on the weird state that exists today - which would also be fixable with another property/bit without too much difficulty)