Add more complex opengl examples

[blockspacer]

See https://github.com/blockspacer/imgui-qtquick-wasm-port

Integration of Dear ImGui 1.66b with Qt Quick, works with QT for WebAssembly (ported without utf8 fonts)

Uses #include <QOpenGLContext>

[blockspacer]

See https://github.com/blockspacer/qtimgui-wasm-port.git

qt for webassembly port of qtimgui (demo-window works) https://github.com/seanchas116/qtimgui (ported without utf8 fonts)

Uses opengl:
#include <GLES2/gl2.h>

demo-window works, but demo-widget prints error:
QOpenGLWidget is not supported on this platform.

[msorvig]

You can apply this patch to enable QOpenGLWidget: https://codereview.qt-project.org/#/c/257158/

Though as stated, the code might not be 100% ported to WebGL yet.