Optimize transform propagation for dynamic scenes

[aevyrie]

Objective

• Follow up from previous transform optimization (Transform Propagation Optimization: Static Subtree Marking #18589), make the mark_dirty_trees system more intelligent - don't run this expensive static scene optimization for dynamic scenes.
• Using a threshold was mentioned as a follow up in that PR, and we also want this threshold to be user-configurable.
• This was not implemented previously because the optimizations were still large improvements even in dynamic scenes thanks to the improved parallelism Parallel Transform Propagation #17840

Solution

• Don't run static scene optimization (dirty tree tracking) for very dynamic scenes - defined here as scenes where more than 30% of objects have their Transform updated.
• This is configurable with a percentage threshold, or it can be unconditionally enabled or disabled when setting to 0.0 or 1.0 to avoid the cost of computing the threshold.
• For dynamic scenes, this makes transform prop much faster, twice as fast in the stress tests shown here.

Testing

transform_hierarchy stress tests, all of these cases spawn about a quarter million entities:

• humanoids_active - dynamic scene that should be faster than main:

• humanoids_inactive - static scene that should be unchanged from main:

• humanoids_mixed - half dynamic scene that should be faster than main

• large_tree - dynamic scene (50% of entities are moved) we expect to see improvements

[cart]

Potentially very large performance wins at the cost of checking every transform's change state an additional time each frame (when enabled). Compelling numbers. Straightforward impl. Sign me up!