Replace TextChar types with traits

[caleb-allen]

The TextUtils submodule defines TextChar, whose subtypes are wrappers around Char. The types themselves aren't really necessary, and it might offer clarity to refactor the many junction_type methods to use traits rather than these TextChar subtypes

VimBindings.jl/src/textutils.jl

Line 74 in 6e4e07d

abstract type TextChar end

The package WhereTraits.jl may be a good fit here. I haven't looked under the hood so I don't know how it affects performance; my main concern is that it will hamper performance, but it may not be an issue.