report terminal size on Windows

[mattn]

add new func term_report_winsize.

[codecov-io]

Codecov Report

Merging #1863 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1863      +/-   ##
==========================================
+ Coverage   75.06%   75.07%   +<.01%     
==========================================
  Files          76       76              
  Lines      125238   125239       +1     
==========================================
+ Hits        94014    94020       +6     
+ Misses      31224    31219       -5

Impacted Files	Coverage Δ
src/gui_beval.c	43.96% <0%> (-0.93%)	⬇️
src/if_xcmdsrv.c	83.33% <0%> (-0.56%)	⬇️
src/if_py_both.h	76.02% <0%> (ø)	⬆️
src/undo.c	81.64% <0%> (+0.06%)	⬆️
src/channel.c	83.69% <0%> (+0.09%)	⬆️
src/message.c	68.3% <0%> (+0.4%)	⬆️

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