closes #753

• adds an overlay render pass, I think pygfx plans for a more effiicent overlay render pass later without the depth buffer but I think we can update it to that later when it's available.
• Tooltip class that can manage displaying tooltips for registered Graphics
  • Figure.tooltip_manager is an Tooltip instance
• Figure.show_tooltip is a settable property
• Figure.tooltip_manager.register() is a method than can be used for customizable registration of tooltips.

Usage options:

Auto-register all Graphics that will be added to the figure. Tooltips display the data of the hovered vertex or image array element (either grayscale value or RGB(A) values).

fig = fpl.Figure(..., show_tooltips=True)

# to hide tooltips for all graphics in an existing Figure
# this basically unregisters all graphics
# figure.show_tooltips = False

# to show tooltips for all graphics in an existing Figure
# this basically registers all current graphics in the figure's subplots
# figure.show_tooltips = True

Manually register a tooltip for a Graphic.

fig.tooltip_manager.register(
    graphic=my_graphic,
    appear_event="click",  # any valid pointer event
    disappear_event="double_click",  # any valid pointer event
)

Manually register a tooltip to show custom info by register a function that takes the pointer event and returns a str:

def custom_tooltip_info(ev: PointerEvent):
    index = ev.pick_info["vertex_index"]
    info = custom_metadata_object[index]
    return info

fig.tooltip_manager.register(
    my_graphic,
    custom_info=custom_tooltip_info,
)