Lrlex codegen

[ratmice]

This is an attempt at lrlex codegen, in the style of the recently added lrpar codegen module.
One thing this doesn't do is change the CTTokenMapBuilder.

This tries to sequence the move over a couple of commits, with the first commit just generating module and ownership structure. With each subsequent commit moving one aspect of code generation, until it's all in the codegen module.

One slightly suprising thing was the placement of lexerdef within the LexerBuildEnv, because we need it to generate the rule_ids_map, with that we can wait to generate the LexerCodegen util the rule_ids_map is built, and pass it in to the code_generator function, this is a slight departure from the lrpar api, which merely took a timestamp.

Edit: One thing that the additional rule_ids_map parameter I immediately notice is that unlike BuildEnvArgs and other builder patterns, it's hard for us to add add an additional parameter should we need one. I wonder if we should consider LexerCodegenArgs?

[ratmice]

I had forgotten to double check this, for some reason I thought a variant had been added to this,
but that was LexerCodegenError.

[ratmice]

This wacky map_err/match was necessary at the time because ? couldn't convert the error.
I figured by the time I was done we'd have a variant added. Although I must admit I'm a bit uncertain what the type returned is, I assume it's inferring ! or some such.