Add value_input to TextInput widgets

[philippjfr]

Fixes #1882

[codecov]

Codecov Report

Merging #2007 (bff7e91) into master (fd9e09c) will decrease coverage by 0.00%.
The diff coverage is 96.96%.

@@            Coverage Diff             @@
##           master    #2007      +/-   ##
==========================================
- Coverage   84.81%   84.81%   -0.01%     
==========================================
  Files         166      166              
  Lines       19997    20000       +3     
==========================================
+ Hits        16961    16962       +1     
- Misses       3036     3038       +2     

Impacted Files	Coverage Δ
panel/tests/test_reactive.py	98.88% <95.00%> (+0.07%)	⬆️
panel/widgets/input.py	95.83% <100.00%> (-0.04%)	⬇️
panel/widgets/select.py	93.51% <100.00%> (+0.02%)	⬆️
panel/io/reload.py	65.88% <0.00%> (-2.36%)	⬇️
panel/pane/vtk/vtk.py	96.39% <0.00%> (-0.03%)	⬇️
panel/pane/vtk/synchronizable_deserializer.py	97.58% <0.00%> (+0.03%)	⬆️

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