Error message for missing browser executables should be friendlier

[coreyti]

A trace example:

** (FunctionClauseError) no function clause matching in Playwright.Browser.new_page/2
    (playwright 1.18.0-alpha.1) lib/playwright/browser.ex:153: Playwright.Browser.new_page({:error, %Playwright.Channel.Error{message: "Executable doesn't exist at <redacted>/chrome-mac/Chromium.app/Contents/MacOS/Chromium"}}, %{})
    <redacted>
    (elixir 1.13.2) lib/task/supervised.ex:89: Task.Supervised.invoke_mfa/2
    (elixir 1.13.2) lib/task/supervised.ex:34: Task.Supervised.reply/4
    (stdlib 3.17) proc_lib.erl:226: :proc_lib.init_p_do_apply/3