Backends: OpenGL: Partially revert 1.86 change of using glBufferSubData(): now only done on Intel GPUs. (#4468, #3381, #2981, #4825, #4832, #5127)

Essentially reverts 389982eb for non-Intel GPUs + update imgui_impl_opengl3_loader.h
Amended once (force-pushed).

backends/imgui_impl_opengl3_loader.h

@@ -164,6 +164,8 @@ typedef khronos_uint8_t GLubyte;
 #define GL_FLOAT                          0x1406
 #define GL_RGBA                           0x1908
 #define GL_FILL                           0x1B02
+#define GL_VENDOR                         0x1F00
+#define GL_RENDERER                       0x1F01
 #define GL_VERSION                        0x1F02
 #define GL_EXTENSIONS                     0x1F03
 #define GL_LINEAR                         0x2601