Fix y billboard shear when rotating camera

Fixes shear effect with `BILLBOARD_FIXED_Y` when the camera is rotated around the z-axis by rotating the mesh correctly into view space.

Also removes shearing effects that occur when rotating the mesh by excluding the model rotation and scale from the billboard matrix.

scene/resources/material.cpp

@@ -790,12 +790,10 @@ void BaseMaterial3D::_update_shader() {
 			}
 		} break;
 		case BILLBOARD_FIXED_Y: {
-			code += "	MODELVIEW_MATRIX = INV_CAMERA_MATRIX * mat4(CAMERA_MATRIX[0],WORLD_MATRIX[1],vec4(normalize(cross(CAMERA_MATRIX[0].xyz,WORLD_MATRIX[1].xyz)), 0.0),WORLD_MATRIX[3]);\n";
+			code += "	MODELVIEW_MATRIX = INV_CAMERA_MATRIX * mat4(vec4(normalize(cross(vec3(0.0, 1.0, 0.0), CAMERA_MATRIX[2].xyz)),0.0),vec4(0.0, 1.0, 0.0, 0.0),vec4(normalize(cross(CAMERA_MATRIX[0].xyz, vec3(0.0, 1.0, 0.0))),0.0),WORLD_MATRIX[3]);\n";
 
 			if (flags[FLAG_BILLBOARD_KEEP_SCALE]) {
-				code += "	MODELVIEW_MATRIX = MODELVIEW_MATRIX * mat4(vec4(length(WORLD_MATRIX[0].xyz), 0.0, 0.0, 0.0),vec4(0.0, 1.0, 0.0, 0.0),vec4(0.0, 0.0, length(WORLD_MATRIX[2].xyz), 0.0), vec4(0.0, 0.0, 0.0, 1.0));\n";
-			} else {
-				code += "	MODELVIEW_MATRIX = MODELVIEW_MATRIX * mat4(vec4(1.0, 0.0, 0.0, 0.0),vec4(0.0, 1.0/length(WORLD_MATRIX[1].xyz), 0.0, 0.0), vec4(0.0, 0.0, 1.0, 0.0),vec4(0.0, 0.0, 0.0 ,1.0));\n";
+				code += "	MODELVIEW_MATRIX = MODELVIEW_MATRIX * mat4(vec4(length(WORLD_MATRIX[0].xyz), 0.0, 0.0, 0.0),vec4(0.0, length(WORLD_MATRIX[1].xyz), 0.0, 0.0),vec4(0.0, 0.0, length(WORLD_MATRIX[2].xyz), 0.0),vec4(0.0, 0.0, 0.0, 1.0));\n";
 			}
 		} break;
 		case BILLBOARD_PARTICLES: {