Add firenvim#write() function enabling users to write arbitrary data

The goal of this commit is to enable the use case desired by #1589. This
isn't a perfect fit as the user was asking for a way to setup
post-processing of their text instead of having to call firenvim#write,
but as I am on a tight schedule for publishing a new release I do not
have time for further discussions, and following the pattern of
firenvim#hide_frame, firenvim#eval_js, firenvim#focus_* feels like a
very safe choice.

autoload/firenvim.vim

@@ -50,6 +50,22 @@ function! firenvim#hide_frame() abort
         call rpcnotify(firenvim#get_chan(), 'firenvim_hide_frame')
 endfunction
 
+" Asks the browser extension to hide the firenvim frame
+function! firenvim#write(...) abort
+        let l:text = ""
+        let l:cursor = [0, 0]
+        if len(a:000) == 0
+                let l:text = nvim_buf_get_lines(0, 0, -1, 0)
+                let l:cursor = nvim_win_get_cursor(0)
+        elseif len(a:000) == 2
+                let l:text = a:0
+                let l:cursor = a:1
+        else
+                throw "firenvim#write should be called either with 0 arguments or with 2 arguments (string, [number, number])"
+        endif
+        call rpcnotify(firenvim#get_chan(), 'firenvim_bufwrite', {"text": l:text, "cursor": l:cursor})
+endfunction
+
 " Asks the browser extension to send one or multiple key events to the
 " underlying input field.
 function! firenvim#press_keys(...) abort

src/frame.ts

@@ -118,14 +118,7 @@ export const isReady = browser
                   group = group,
                   pattern = filename,
                   callback = function(ev)
-                    vim.fn.rpcnotify(
-                      channel,
-                      "firenvim_bufwrite",
-                      {
-                        text = vim.api.nvim_buf_get_lines(0, 0, -1, 0),
-                        cursor = vim.api.nvim_win_get_cursor(0)
-                      }
-                    )
+                    vim.fn["firenvim#write"]()
                   end
                 })
                 vim.api.nvim_create_autocmd("VimLeave", {