Fix Clear REPL when using bracketed_paste_python formatter

[g0t4]

When using bracketed_paste_python with ipython and python3 the formatter calls remove_empty_lines which replaces FF with CR

https://github.com/g0t4/iron.nvim/blob/d8c2869/lua/iron/fts/common.lua#L119-L120

I split out a new core.clear_repl function, similar to core.close_repl and in there I bypass using .send_to_repl and instead go to chansend directly.

I have not yet investigated the implications for this on Windows, I am happy to help with that if this is the right direction to go with a fix for this.

And if I am not doing something else wrong.

Btw, clear works fine for lua and other REPLs that don't override the formatter.