[client] egl: switch to using GL_TEXTURE_EXTERNAL_OES for DMABUF

According to Erik @ NVidia the open source NVidia driver will not
create a EGLImage from a DMABUF if the target is not
GL_TEXTURE_EXTERNAL_OES. This change set converts the dmabuf texture
from GL_TEXTURE_2D to GL_TEXTURE_EXTERNAL_OES and at runtime performs a
global search & replace on fragment shaders as needed to remain
compatible, replacing `sampler2D` with `samplerExternalOES`.

Ref: https://github.com/NVIDIA/open-gpu-kernel-modules/discussions/243#discussioncomment-3283415

client/renderers/EGL/texture.h

@@ -93,6 +93,9 @@ typedef struct EGL_TextureOps
 
   /* get the texture for use */
   enum EGL_TexStatus (*get)(EGL_Texture * texture, GLuint * tex);
+
+  /* bind the texture for use */
+  enum EGL_TexStatus (*bind)(EGL_Texture * texture);
 }
 EGL_TextureOps;