If you are okay with using Physics2DDirectSpaceState (as seen here), then you can use the intersect_point function to get the collider the mouse is over (untested):
extends Node2D
func _physics_process(delta):
var space_state = get_world_2d().direct_space_state
var mouse_collision_info = space_state.intersect_point(get_global_mouse_position())
if (mouse_collision_info.empty() == false):
for info in mouse_collision_info:
print ("Mouse is inside node with name: ", collider.name)
