CastFromBool: support untyped bool

[xushiwei]

No description provided.

[codecov-commenter]

Codecov Report

Merging #168 (164024d) into main (c3d4c64) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #168      +/-   ##
==========================================
+ Coverage   94.83%   94.84%   +0.01%     
==========================================
  Files          15       15              
  Lines        5944     5956      +12     
==========================================
+ Hits         5637     5649      +12     
  Misses        236      236              
  Partials       71       71              

Impacted Files	Coverage Δ
ast.go	94.91% <100.00%> (+0.03%)	⬆️
type_var_and_const.go	98.63% <100.00%> (+0.02%)	⬆️

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