fix(frontends/lua): make sure Lua 'sleep' function support interruption

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(frontends/lua): rename leanlua_state to script_state, and move it to util

This commit also minimizes the dependencies of script_state.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(frontends/lua): rename leanlua_state to script_state, and move it to util