ImFont: small optimization to our (incorrect) handling of TAB
ImFont: small optimization to our (incorrect) handling of TAB

TAB is still handled as 4-spaces width (which is incorrect)
But CalcTextSize is simplified.

kylawl/imgui,ocornut/imgui,Flix01/imgui,thennequin/imgui,Psybrus/imgui,kylawl/imgui,seanmiddleditch/imgui,burningreggae/imgui,xunmengfeng/imgui,neshume/imgui,sakishum/imgui,DXsmiley/FlexGUI,cmaughan/imgui,ocornut/imgui,Extrawurst/imgui,zho7611/imgui,neshume/imgui,gyakoo/imgui,rmoorman/imgui,aimotive/imgui-glfw,Pagghiu/imgui,rmoorman/imgui,andresv/imgui,redblobgames/imgui,emoon/imgui,tpoechtrager/imgui,Psybrus/imgui,dougbinks/imgui,rxantos/imgui,seanmiddleditch/imgui,burningreggae/imgui,shaggytwodope/imgui,aimotive/imgui-glfw,luiseduardohdbackup/imgui,benoitjacquier/imgui,cmaughan/imgui,wflohry/imgui-addons,tom-seddon/imgui,sakishum/imgui,GHF/imgui,gamedeff/imgui,wflohry/imgui-addons,nProtect/imgui,usagi/imguixx,luiseduardohdbackup/imgui,dougbinks/imgui,wangshijin/imgui,xythobuz/imgui,usagi/imguixx,thevaber/imgui,ggtucker/imgui,twigletguy/imgui,nmlgc/imgui,Pagghiu/imgui,thennequin/imgui,gyakoo/imgui,bkaradzic/imgui,zho7611/imgui,Extrawurst/imgui,ghassanpl/imgui,cmaughan/imgui,wasikuss/imgui,mikesart/imgui,Flix01/imgui,benoitjacquier/imgui,Flix01/imgui,ggtucker/imgui,redblobgames/imgui,ghassanpl/imgui,tom-seddon/imgui,DXsmiley/FlexGUI,tpoechtrager/imgui,bagobor/imgui,nProtect/imgui,bkaradzic/imgui,nmlgc/imgui,wangshijin/imgui,xunmengfeng/imgui,emoon/imgui,twigletguy/imgui,GHF/imgui,bagobor/imgui,xythobuz/imgui,rxantos/imgui,gamedeff/imgui,shaggytwodope/imgui,cmaughan/imgui,thevaber/imgui,ocornut/imgui,mikesart/imgui,nProtect/imgui,elect86/imgui,andresv/imgui,elect86/imgui,ggtucker/imgui,wasikuss/imgui,bkaradzic/imgui