Fix explosion damage on players

[Flonja]

Calculations taken from decompiled java edition, but it seems to match bedrock values
(Edited slightly to make the original code easier to read)

                float d = this.radius * 2.0F;
                double dist = entity.distanceTo(vec3d); // Same as `entity.Sub(vec3d).Len()`

                if (dist / d <= 1.0D) {
//                    double d8 = entity.getX() - this.x;
//                    double d9 = (entity instanceof EntityTNTPrimed ? entity.getY() : entity.getEyeY()) - this.y;
//                    double d10 = entity.getZ() - this.z;
//                    double d11 = Math.sqrt(d8 * d8 + d9 * d9 + d10 * d10); // Same as `dist`

                    if (dist != 0.0D) {
                        double exposure = (double) getSeenPercent(vec3d, entity); // Same as `exposure(vec3d, entity)`
                        double impact = (1.0D - dist) * exposure;
                        entity.hurt(this.getDamageSource(), (float) ((int) ((impact * impact + impact) / 2.0D * 7.0D * (double) d + 1.0D)));