Allow C-r to insert register contents in prompts and pickers

[EpocSquadron]

We currently have the ability to insert the contents of any register in insert mode in the buffer. However, it is often useful to do so in search prompts, or the command prompt, and even in pickers.

One example is using * to add the current selection to the / register, then invoking a global search. When the global search prompt pops up, you would uae Ctrl-r/ to fill the prompt with the search buffer, then enter. Otherwise you need to type out the whole search term even though you know you had it selected already, or else resort to using system clipboard to get around it.

Another example might be copying a namespace that's close to a file path but not quite (so gf isn't enough), then placing it in the picker prompt to allow fuzzy matching to pull up the correct path.