Allow bind to extract dependencies and evaluate other dynamic functions

[philippjfr]

Allows binding another dynamic function:

slider = pn.widgets.IntSlider(value=2, start=0, end=10)
slider2 = pn.widgets.IntSlider(value=4, start=0, end=10)
slider3 = pn.widgets.IntSlider(value=2, start=0, end=10)

def add(a, b):
    return a + b

def divide(a, b):
     return a / b

bound = pn.bind(divide, pn.bind(add, slider, slider2), slider3)
assert bound() == 3

[codecov]

Codecov Report

Merging #2056 (acca37e) into master (85a1392) will increase coverage by 0.01%.
The diff coverage is 95.00%.

@@            Coverage Diff             @@
##           master    #2056      +/-   ##
==========================================
+ Coverage   84.43%   84.44%   +0.01%     
==========================================
  Files         178      178              
  Lines       20636    20670      +34     
==========================================
+ Hits        17423    17455      +32     
- Misses       3213     3215       +2     

Impacted Files	Coverage Δ
panel/depends.py	83.82% <90.00%> (+0.49%)	⬆️
panel/tests/test_depends.py	100.00% <100.00%> (ø)

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[jbednar]

Cool!