[Imgui] Update docking-experimental and freetype features to 1.81

[RT2Code]

Update the docking-experimental feature from 1.79 to 1.81.

The Freetype integration procedure was changed with 1.81, the IMGUI_ENABLE_FREETYPE macro should be defined in imconfig.h.

• We refactored some of imgui_freetype to make integration easier (a simple #define IMGUI_ENABLE_FREETYPE in your config file does the job for most users) and also to fix some inconsistencies. The majority of imgui_freetyoe users shouldn't be affected as the RasterizerFlags were rarely used.
• Removed ImGuiFreeType::BuildFontAtlas(). Kept inline redirection function.
• Prefer using #define IMGUI_ENABLE_FREETYPE, but there's a runtime selection path available too.
• The shared extra flags parameters (very rarely used) are now stored in ImFontAtlas::FontBuilderFlags.
• Renamed ImFontConfig::RasterizerFlags (used by FreeType) to ImFontConfig::FontBuilderFlags.
• Renamed ImGuiFreeType::XXX flags to ImGuiFreeTypeBuilderFlags_XXX for consistency with other API.

I updated the CMake file to uncomment this macro in imconfig.h when the user ask for the freetype feature.

[NancyLi1013]

The regressions caused by gsoap will be fixed by PR #16270.

[ras0219-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ras0219-msft]

Editing the sources during configure causes a race condition if we configure release and debug in parallel, so I've moved the edit to the portfile as a post-build step.

As a drive-by, I've changed the versioning scheme to relaxed which will enable our new versioning features.

This LGTM, though I'd appreciate independent confirmation from @RT222 that this still fixes their issue :)

Thanks for the PR!

[RT2Code]

The IMGUI_ENABLE_FREETYPE macro should only be defined in imconfig.hpp when the freetype feature is enabled, I fixed it. I also moved the string replacement code for wchar32 to the portfile for the reasons you mentioned about parallel configuration.