imgui 1.90.6 -> 1.91.6

[briaguya-ai]

decided to handle the breaking ImTextureID change by patching imconfig.h to have

#define ImTextureID void*

to switch us back to what we had before (which is working)

note: i early merged #789 into this branch to get green checks on linux builds

soh pr:

• imgui 1.90.6 -> 1.91.6 HarbourMasters/Shipwright#4838

edit: moved to draft, trying another thing
edit: other thing worked, moving back out of draft

stuff from before the `imconfig` patching

most of these changes are from 9b6a91e where i mentioned

in ocornut/imgui@92b9498 ImTextureID was updated from void* to ImU64, which is defined as unsigned long long (which conflicts with some implementations of uint64_t that have it as unsigned long)

i linked some info on this and some other breaking changes in #770

i'm very open to feedback/ideas on how to handle this ImGui change - i know we have some other options but this one seemed reasonable

[Archez]

Changes look sensible to me