Optimize shared texture creations

[ze2j]

Fix #98733

This PR removes an unnecessary copy of Texture::slice_trackers, as it is always cleared afterward.

Build: scons platform=linuxbsd optimize=speed_trace debug_symbols=yes
Profiler: Tracy
Test project: see MRP in #98733

Results with master branch:

Results with this PR:

[clayjohn]

I guess duplicate_as_shared_resource should also avoid copying shared_fallback so we don't have to manually set it to nullptr right after doing the copy

[clayjohn]

I find it a bit surprising that we don't call texture.slice_trackers.clear(); here.

CC @DarioSamo who added the call in texture_create_shared(). Do you think this was missed by mistake? Or is there a reason to maintain the slice_tracker when creating a shared texture from a slice?

[ze2j]

The clear is made in _texture_make_mutable

[DarioSamo]

I think slice_trackers should be turned into a pointer instead and allocate it on demand only if a shared texture is created. The HashMap currently occupies 48 bytes per texture and largely goes unused in the vast majority of cases. Then when the copy is made, the simple solution is to just set it to a nullptr. That way there'll be no cost from copying the contents as is and we get a reduced memory footprint overall, for the small extra cost of an indirection.

I'm not a big fan of the proposed solution as it adds another function to maintain and keep track of when the copy is made.

[ze2j]

I agree and I am not a big fan of my solution too : ) I am going to rework my PR with your solution, it's a nice idea.