This change makes it so motion paths are using minimal possible dependency graph which is sufficient to evaluate required motion path targets. Disclaimer: granularity is done on ID level, but it is possible to go more granular if really needed. Brings time down to 0.5 sec when updating motion path for the Rain animation file used for benchmarks in the previous commits. Reviewers: brecht Differential Revision: https://developer.blender.org/D5874