feat: add IMGUI_USE_WCHAR32 support, cross-compile natives, publish to mvn.mrlokop.dev

- Enable IMGUI_USE_WCHAR32 in imconfig.h (ImWchar = uint32_t)
- Extend ImFontGlyphRangesBuilder, ImFontConfig, ImFontAtlas for 32-bit codepoints
- Cross-compile natives for macOS universal, Linux x86_64 (glibc), Windows x86_64
- Publish as org.nnstd.imgui:...:1.90.0-wchar32+mrlokop2 to mvn.mrlokop.dev
- Add BUILDING.md with full rebuild and publish instructions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

build.gradle

@@ -8,7 +8,7 @@ ext {
 
 allprojects {
     group = 'imgui-java'
-    version = 'git describe --tags --always'.execute().text.trim().substring(1)
+    version = '1.90.0-wchar32+mrlokop2'
 
     repositories {
         mavenCentral()