[lldb] Add -l/--language option to script command

Make it possible to run the script command with a different language
than currently selected.

  $ ./bin/lldb -l python
  (lldb) script -l lua
  >>> io.stdout:write("Hello, World!\n")
  Hello, World!

When passing the language option and a raw command, you need to separate
the flag from the script code with --.

  $ ./bin/lldb -l python
  (lldb) script -l lua -- io.stdout:write("Hello, World!\n")
  Hello, World!

Differential revision: https://reviews.llvm.org/D86996