REPL: implement "insert last word from previous history entry"

[rfourquet]

Bind this shell-like feature to the usual "meta-.".

For example, if the previous input was julia> 1 + 2, then <Alt-.> (or <meta-.>) will insert 2 in the current input.

It's not necessary clear what the "last word" should mean. I think that in shells this command considers space-separated words, and also IPython. But the problem is that if the last input is e.g. f(a, b), then the last word is b), which is not very useful. So here I use a slightly different heuristic: go to the end of line, then one word backward (position reaches "before b"), then one word forward (position is between "b" and ")"). Call word what we have jumped around till now (b) and rest what is between current position and the en of line ()). If rest contains a balanced number of parenthesis and brackets, and doesn't contain special characters (`, ", ' for now), then return word * rest, otherwise word. In this example, this would return b, and with 1+f() it would return f().

But most of the time when I try to reach out to this shortcut, it's for simple things which are unambiguous, like when I do for example pkg> up MyPackage and then pkg> st <Alt-.>, or using <Alt-.>, where <Alt-.> would insert MyPackage. Or for example using Random followed by <M-.>.seed!().

This implements the last missing feature from #8447.

[rfourquet]

I will just merge this. The specific behavior can be refined later if needed using input from users.