EMI: Implement Lua_V2::SetActorLocalAlpha

- sets the alpha mode and the alpha value for single vertices

- fixes the issue that the fuse in the first scene on the ship doesn't fully vanish (it partly re-appears) when it burns down

- implemented for OpenGL and works without any problems
- implemented also for TinyGL, but doesn't work here although the alpha values seems to be correctly set
ARGH - good catch! The original code https://github.com/chkr-private/residualvm/commit/84c6041a5f0d081422d53f36f7ef454f25b78272 was OK, it got lost during refactoring. Fixed.