bug#55096: Eldoc showing elisp variable value beside docs

[emacsq]

Eldoc showing the docs in the minibuffer is quite useful, but I often check elisp variable values too in the code, and it can be quite handy if eldoc shows that too simply by putting cursor on the variable.

So for variables the value too can  be shown after the docs. In case of primitive values it's quite simple, if there is a local value then it can show  the local  value first and then the global one.

In case of complex values the full value may be too big to display, but the beginning of it can still be shown, truncated after, say, 30 chars. It is still useful if, for example, a variable can be nil and also a list. Then you can see at a glance if it has a value set.