Is it possible to keep `REPL.REPLDisplay` as default?

When using default sysimg it's shown in REPL that
```jl
julia> Base.Multimedia.displays[2]
REPL.REPLDisplay{LineEditREPL}(LineEditREPL(REPL.Term...
```
However if a package define a display (eg. `Cobweb.CobwebDisplay()`) then after `create_sysimage` of the package, the `REPLDisplay` would not stay as the second item on the list when using the customized sysimg. So the environment is different from the manual one, i.e., default sysimg -> entering REPL -> using the package.

Reproduce the comparison between a default sysimg and a package-created sysimg, inspecting Base.Multimedia.displays[2] after entering the REPL. Trace the create_sysimage path and REPL display initialization; done means a customized sysimg keeps REPL.REPLDisplay as the second display even when a package defines its own display.

Written by the indexing model from the issue text.