Allow to run client without RStudio Viewer

[ColinFay]

Especially when running chrome in non headless mode, we get the Viewer + the browser:

This PR allows to get the client without opening the Viewer:

library(crrri)
chrome <- Chrome$new(
  pagedown::find_chrome(),
  debug_port = 12358L, 
  headless = FALSE
)
client <- chrome$connect(callback = function(client) {
  client$inspect(viewer = FALSE)
})

Page <- client$Page
Runtime <- client$Runtime
Page$navigate(url = "http://google.com")

chrome$close()

Might also be useful when using {crrri} as a tool for testing web app.

[cderv]

I agree with Romain, this

client <- chrome$connect(callback = ~ NULL)

is the way to go get back the client, and not the promises.

If you don't want to get the inspector in the viewer, don't use it as callback and use another callback.