* AstGen: add missing `break_inline` for comptime blocks.
 * Module: call getTree() in byteOffset(). This generates the AST when
   using cached ZIR and compile errors need to be reported.
 * Scope.File: distinguish between successful ZIR generation and AIR
   generation (when Decls in scope have been scanned).
   - `semaFile` correctly avoids doing work twice.
 * Implement first pass at `lookupInNamespace`. It has various TODOs
   left, such as `usingnamespace`, and setting up Decl dependencies.