### Godot version

4.2 RC2

### System information

Any

### Issue description

AnimationMixer separates the accuracy of how discrete keys are retrieved when seeking between internal seeking and external seeking. FYI: https://github.com/godotengine/godot/pull/80708.

Since AnimationPlayer currently treats everything as an internal seek, so it needs to propagate the external seek information.

### Steps to reproduce

Seek AnimationTrackEditor

### Minimal reproduction project

[gd_anim_unittest_1.zip](https://github.com/godotengine/godot/files/13492063/gd_anim_unittest_1.zip)

if (!backwards && prev_pos <= len && next_pos == len) {
				
				end_reached = true;
				end_notify = prev_pos < len; 
				p_blend = 1.0;
			}
			if (backwards && prev_pos >= 0 && next_pos == 0) {
				
				end_reached = true;
				end_notify = prev_pos > 0; 
				p_blend = 1.0;
			}
		}
	}
	PlaybackInfo pi;
	if (p_started) {
		pi.time = prev_pos;
		pi.delta = 0;
		pi.seeked = true;
	} else {
		pi.time = next_pos;
		pi.delta = delta;
		pi.seeked = p_seeked;
	}
	pi.is_external_seeking = false;
	pi.looped_flag = looped_flag;
	pi.weight = p_blend;
	make_animation_instance(cd.from->name, pi);
}
void AnimationPlayer::_blend_playback_data(double p_delta, bool p_started) {