Dynamically update actor trajectories

[chapulina]

Here is an idea for how to expose skeleton control to systems. Currently, actors can only be controlled from the SDF <script>. With these components, systems should have the flexibility to control actors in various different ways. The only thing missing is a way for a system to set waypoints that are automatically interpolated, but I'm not sure how useful that would be.

➡️ ✔️ components::Pose

• Implemented on this PR
• Defines the reference point for all trajectory waypoints (i.e. origin).
• Initialized to <actor><pose>.
• Already merged into Dome.
• Works whether ScriptFromSdf or not.

➡️ components::ScriptFromSdf

• Defaults to true
• If false, the entire <script> from SDF is ignored.
• If set back to true, SDF script starts working again.

➡️ ✔️ components::TrajectoryPose

• Added on this PR (and this declined one)
• Defines the pose of the root bone with respect to components::Pose.
• If ScriptFromSdf, it will be set according to the current interpolation between <waypoint><pose>s.
• If not ScriptFromSdf, unlike <waypoint><pose>, it's not interpolated from the previous pose and performs teleportation.

➡️ ✔️ components::AnimationName

• Name of animation being currently played.
• If ScriptFromSdf, it will be set according to the current <trajectory type> (i.e. <animation name>).
• It must correspond to one of the <animation>s loaded with the SDF.

➡️ ✔️ components::AnimationTime

• Time within animation being currently played.
• If ScriptFromSdf, it will be set according to the animation being currently played.
• If not ScriptFromSdf, BoneTransforms will be ignored and the render engine is responsible for animating them.

➡️ components::UseBoneTransforms

• Defaults to false
• If true, bone transformations will be calculated by Ignition Common and set through the BoneTransforms component.
• If false, the BoneTransforms component is ignored and the render engine is responsible for calculating the transforms based on AnimationName and AnimationTime.

➡️ components::BoneTransforms

• The transformations for each bone in the skeleton, with respect to the root bone.
• If not UseBoneTransforms, it's ignored
• If ScriptFromSdf, it will be set according to the animation being currently played.
• If not ScriptFromSdf, it can be set by other systems to control bones directly.