Paint.setXYZ methods doesn't accept nullptr (None)

Describe the bug
Several setter methods of skia.Paint are documented to accept nullptr to remove the filter/effect from the paint. However, this is not the case as passing None to these methods throws a type error. This is because these methods are pybind-ed with a lambda function. The methods listed below have this problem.

To Reproduce
Steps to reproduce the behavior:
Run the following code

import skia

paint = skia.Paint(
    ImageFilter=skia.ImageFilters.Blur(1.0, 1.0),
    ColorFilter=skia.LumaColorFilter.Make(),
    MaskFilter=skia.MaskFilter.MakeBlur(skia.kNormal_BlurStyle, 1.),
    PathEffect=skia.DashPathEffect.Make([2., 1.], 0),
    Shader=skia.Shaders.Empty(),
)

print(paint.getImageFilter())  # prints <skia.ImageFilter object at 0x...>
paint.setImageFilter(None)  # this works
print(paint.getImageFilter())  # prints None

paint.setColorFilter(None)  # fails with TypeError: setColorFilter(): incompatible function arguments. The following
                            # argument types are supported: # 1. (self: skia.Paint, colorFilter: SkColorFilter) -> None
paint.setMaskFilter(None)  # fails with TypeError
paint.setPathEffect(None)  # fails with TypeError
paint.setShader(None)  # fails with TypeError

Expected behavior
Each of these methods should accept None, execute without error, and remove the corresponding filter/effect.

Desktop (please complete the following information):

• OS: Ubuntu 20.04.1 LTS
• Python: 3.8
• skia-python version: 87.3

Additional context
Note that paint.setImageFilter(None) works as expected. This is because setImageFilter is not pybind-ed with a lambda function.

Start by locating the pybind lambda bindings for Paint.setColorFilter, setMaskFilter, setPathEffect, and setShader, comparing them with setImageFilter, which already accepts None. Reproduce the issue with the provided Python example, then verify that each listed setter accepts None and removes its filter or effect without a type error.