refactor(ast_codegen): move away from RType in generators.

[rzvxa]

This PR introduces EarlyCtx and LateCtx in place of the old CodegenCtx, Early passes operate at the AST level while generators and other late passes operate on the schema.

It will also replace the confusing RType name with something more idiomatic (open for suggestions, I haven't found a good name yet) I've named it AstType and dropped the R prefix for REnum and RStruct.

There are some qualities of life improvements too, Things like to_type_elide can be used to simplify the code.

Related to #4442 (and can potentially mark it "close as fixed").

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[rzvxa]

• feat(ast_codegen, span): process SourceType through ast_codegen. #4696
• feat(ast_codegen): process AST-related syntax types. #4694
• refactor(ast_codegen): disallow implicit enum discriminants on #[ast] types. #4690
• refactor(ast_codegen): move away from RType in generators. #4682 👈
• refactor(syntax): add explicit enum discriminants to AST related types. #4691
• refactor(ast): add explicit enum discriminants. #4689
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #4682 will not alter performance

_{Comparing 08-06-refactor_ast_codegen_move_away_from_rtype_in_generators (1690a57) with main (e24fb5b)}

Summary

✅ 29 untouched benchmarks

[graphite-app]

Merge activity

• Aug 6, 1:11 PM EDT: overlookmotel added this pull request to the Graphite merge queue.
• Aug 6, 1:20 PM EDT: overlookmotel merged this pull request with the Graphite merge queue.