* module/system/repl/common.scm (repl-default-options): Add
optimization-level and warning-level REPL options.
(repl-optimization-level, repl-warning-level): New accessors,
defaulting to the default level parameters.
(repl-expand): Take target language as keyword argument rather than
hard-coding tree-il.
(repl-optimize): Take target language as keyword argument. Use REPL
optimization and warning levels. Use generic lowering interface.