Fix T92807: Incorrect display planar tracking.

Issue introduced in {7e66616b7e15} where the shader was replaced with a
2d image shader. This patch reverts several commits that removed the 3d
image shader.

source/blender/gpu/GPU_shader.h

@@ -259,6 +259,15 @@ typedef enum eGPUBuiltinShader {
   GPU_SHADER_2D_IMAGE_OVERLAYS_MERGE,
   GPU_SHADER_2D_IMAGE_OVERLAYS_STEREO_MERGE,
   GPU_SHADER_2D_IMAGE_SHUFFLE_COLOR,
+  /**
+   * Draw texture with alpha. Take a 3D position and a 2D texture coordinate for each vertex.
+   *
+   * \param alpha: uniform float
+   * \param image: uniform sampler2D
+   * \param texCoord: in vec2
+   * \param pos: in vec3
+   */
+  GPU_SHADER_3D_IMAGE_MODULATE_ALPHA,
   /* points */
   /**
    * Draw round points with a hardcoded size.