introduce DrawingMode to reduce switching

[koron]

描画モードを集中的に管理することで、
AssureXxxやFlushXxxを呼び出す煩雑さからの脱却を目指した。

合わせて意図せぬモード変更を避けやすくなるはず。

[koron]

mInteropHDC != NULL のチェックをしているところは
mDMode == DM_INTEROP に置き換えたほうが、意味が通りやすいかも。

[codecov]

Codecov Report

Merging #2 into improve-color-emoji will increase coverage by <.01%.
The diff coverage is n/a.

@@                   Coverage Diff                   @@
##           improve-color-emoji       #2      +/-   ##
=======================================================
+ Coverage                74.52%   74.52%   +<.01%     
=======================================================
  Files                       91       91              
  Lines                   132415   132415              
  Branches                 30807    29083    -1724     
=======================================================
+ Hits                     98682    98688       +6     
+ Misses                   33704    33698       -6     
  Partials                    29       29

Impacted Files	Coverage Δ
src/if_xcmdsrv.c	83.63% <0%> (-0.72%)	⬇️
src/gui.c	47.4% <0%> (-0.06%)	⬇️
src/gui_gtk_x11.c	47.65% <0%> (-0.05%)	⬇️
src/terminal.c	64.92% <0%> (+0.06%)	⬆️
src/os_unix.c	54.37% <0%> (+0.13%)	⬆️
src/ex_cmds.c	78.08% <0%> (+0.22%)	⬆️

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[koron]

mDMode == DM_INTEROP に置き換えたほうが、意味が通りやすい

やっといた。

[k-takata]

この { は次の行かな。

[k-takata]

Fixed.