[REPLCompletions] fix #51548, set up a mode to limit the scope of the aggressive inference (#51581)
It turns out that when using `REPLInterpreter` inference for tasks like
evaluating (partially) interpolated paths in shell mode, we need to
ensure accuracy of the inference result, requiring `REPLInterpreter` to
disable its aggressive inference (xref:
<https://github.com/JuliaLang/julia/pull/51581#issuecomment-1749732045>).
To this end, this commit adds an optional argument
`limit_aggressive_inference::Bool=false` to `repl_eval_ex`.
This mode will allow future REPL completion code to utilize it when
prioritizing correct inference results over a wider range of completion
opportunities. Note that that mode is disabled by default, so our
current completion capabilities are preserved.
Fixes #51548.