We don't need this right now but it could be useful in the future, if
anything to detect if Elixir was installed using this installer.
Demo:
iex> {:ok, r} = :win32reg.open([:read])
iex> :win32reg.change_key(r, ~c"\\hklm\\software\\wow6432node\\elixir\\elixir")
iex> :win32reg.value(r, ~c"installroot")
{:ok, ~c"C:\\Program Files\\Elixir"}
1. If we couldn't verify installed OTP, don't quit but let user proceed with installing just Elixir
2. When checking installed OTPs, pick the recent most installed. Previously we were picking the first one which was basically guaranteed to be too old.
3. If we find an existing Elixir installation but it doesn't match the OTP version, offer to download the OTP version this Elixir installer was compiled against (which usually would be the newer version)
4. Add "Verify Erlang/OTP" button which re-checks for installed OTP.
Closes#12678.
Jonatan Männchen
Wojtek Mach