Add throttled argument to pn.param widgets parameter

[hoxbro]

The reason for this PR it is hard to incorporate value_throttled for sliders into a parametrized class.
This will add the possibility to add a throttled argument to pn.param widgets argument. So the following is possible:

import param
import panel as pn


class A(param.Parameterized):
    value_ = param.Range(
        default=(100, 250),
        bounds=(0, 250),
    )
    
    value_throttled_ = param.Range(
        default=(100, 250),
        bounds=(0, 250),
    )
  
    def __init__(self, **params):
        super().__init__(**params)
        widgets = {
            "value_": pn.widgets.IntRangeSlider,
            "value_throttled_": {
                "type": pn.widgets.IntRangeSlider,
                "throttled": True
            },
        }
        self.controls = pn.Param(self, widgets=widgets)

    @param.depends("controls")
    def calculation(self):
        return self.value_, self.value_throttled_


a = A()
pn.Column(a.controls, a.calculation)

To get this to work I'm changing the param object from linking with value to linking with value_throttled of the slider and vice versa. This is only done if throttled is enabled and the widget contains the attribute value_throttled.

This is the reason why the unit test without throttled enabled is on value and with throttled enabled is on value_throttled.

I hope that the configuration of throttled is done as mentioned here.

If there is a better way to implement this, this PR can be closed.

TODO:

• I need some guidance if I need to add more to the unit test.
• Add some documentation for this feature. I think it properly should be located here.

[codecov]

Codecov Report

Merging #1800 (43d4cf2) into master (d67c09d) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1800      +/-   ##
==========================================
+ Coverage   85.13%   85.15%   +0.02%     
==========================================
  Files         151      151              
  Lines       17954    17988      +34     
==========================================
+ Hits        15285    15318      +33     
- Misses       2669     2670       +1     

Impacted Files	Coverage Δ
panel/param.py	90.30% <100.00%> (+0.08%)	⬆️
panel/tests/test_param.py	99.87% <100.00%> (+<0.01%)	⬆️
panel/pane/holoviews.py	83.88% <0.00%> (-0.17%)	⬇️

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[philippjfr]

This looks fabulous, thanks for your efforts around this!