Implement Lua Code Generator using IR

[dbaileychess]

Reference: #6428 (comment)

[dbaileychess]

I'm just marking down things I noticed when implementing this. I haven't investigated these in depth, just wanted to keep track of them.

• Documentation strings don't seem to be populated.
• The sizes of the BaseType are not specified. I know I can imply them, but its probably better if they were explicitly stated.
• There is no information on where to place the generated files (i.e., the -o prefix). Perhaps that should be out of band, but just making note.

[dbaileychess]

• Declaring file is just the root schema file, not the file it was defined in.
• I don't see any way to get namespace, apart from being encoded in the object names themselves.

[dbaileychess]

• I didn't see any padding info for structures.

[dbaileychess]

Solved some of me own issues.

Documentation strings don't seem to be populated.

Need to implicitly set --bfbs-comments

Declaring file is just the root schema file, not the file it was defined in.

I didn't look at a good example, it is the correct declaring file.

I don't see any way to get namespace, apart from being encoded in the object names themselves.

This should be fine as long as the format of dotted namespaces stays the same.