* [imgui] Update docking-experimental and freetype features to 1.81
* [imgui] Update version files
* [imgui] Move string replacement to post-build
* Update ports/imgui/CMakeLists.txt
* [imgui] Declare IMGUI_ENABLE_FREETYPE macro only if the freetype feature is enabled and move wchar32 string replacement to post-build
* [imgui] Update version files
Co-authored-by: Rémy Tassoux <rt2@rasterizedworld.com>
Co-authored-by: Robert Schumacher <roschuma@microsoft.com>
Co-authored-by: Jack·Boos·Yu <47264268+JackBoosY@users.noreply.github.com>