Fix location sync

[hoxbro]

This is a fix to the location sync mentioned in #1784.

I have not done this for any other widgets than DatePicker, because I don´t know if there is a smarter way to do it, if there is let me know. Also need to create unit test for it.

[codecov]

Codecov Report

Merging #1788 (b147e99) into master (b47ca33) will decrease coverage by 0.00%.
The diff coverage is 72.72%.

@@            Coverage Diff             @@
##           master    #1788      +/-   ##
==========================================
- Coverage   85.13%   85.12%   -0.01%     
==========================================
  Files         151      151              
  Lines       17923    17932       +9     
==========================================
+ Hits        15258    15264       +6     
- Misses       2665     2668       +3     

Impacted Files	Coverage Δ
panel/io/location.py	83.78% <50.00%> (-0.62%)	⬇️
panel/widgets/input.py	95.59% <77.77%> (-0.55%)	⬇️

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[philippjfr]

The correct way to do this will be to get this into the param serialization framework.

[philippjfr]

In fact this is already correctly implemented in param, so not quite sure why the deserialize call shouldn't work.