Add EGL-based backend for wxGLCanvas

Among other things, this enables wxGLCanvas to be used natively on
Wayland.

Closes https://github.com/wxWidgets/wxWidgets/pull/2038

Closes #17702.

build/cmake/files.cmake

@@ -3036,11 +3036,13 @@ set(OPENGL_MSW_HDR
 set(OPENGL_GTK_SRC
     src/gtk/glcanvas.cpp
     src/unix/glx11.cpp
+    src/unix/glegl.cpp
 )
 
 set(OPENGL_GTK_HDR
     wx/gtk/glcanvas.h
     wx/unix/glx11.h
+    wx/unix/glegl.h
 )
 
 set(OPENGL_OSX_COCOA_SRC

build/cmake/init.cmake

@@ -385,6 +385,9 @@ if(wxUSE_GUI)
             set(OPENGL_LIBRARIES "-framework OpenGLES" "-framework QuartzCore")
         else()
             find_package(OpenGL)
+            if(WXGTK3 AND OpenGL_EGL_FOUND)
+                set(wxUSE_GLCANVAS_EGL ON)
+            endif()
         endif()
         if(NOT OPENGL_FOUND)
             message(WARNING "opengl not found, wxGLCanvas won't be available")

build/cmake/setup.h.in

@@ -549,6 +549,8 @@
 
 #cmakedefine01 wxUSE_GLCANVAS
 
+#cmakedefine01 wxUSE_GLCANVAS_EGL
+
 #cmakedefine01 wxUSE_RICHTEXT