Continue profiling and reducing GC pressure in Terra Firma.

[bryanedds]

We've cut down GC pressure here a great deal by using the Scitech profiler like so -

This is an effective profiler, but it's hard to learn to use the right way.

[bryanedds]

It might make sense to defer this until after we update to .NET 9 so some of our optimizations could become unnecessary with the new escape analysis optimizations.

[bryanedds]

With .NET 9 and more optimizations, we're down to 0.5mb / frame. .NET 9 only seemed to provide a very tiny of allocation reduction.

[bryanedds]

Unfortunately, the biggest optimizations resulted in regressions with undo / redo. We had revert those bits, which brings us back up to 0.8mb / frame. However, doing a more recent comparison between .NET 8 and 9 shows that we actually got a significant reduction in GC pressure (from 1.1mb to 0.8), so it looks like the object stack allocation is, in fact, doing some useful lifting.