Enhance console_io to permit emits limited in various ways, such as valid UTF-8,...

Enhance console_io to permit emits limited in various ways, such as valid UTF-8, upto control chars, or with counted limits, all getting away from 0-termination as the sole limit. In CLI, use this capability to avoid certain emit-chars-singly procedures that were breaking up UTF-8 characters. This fixes broken json mode output (on Windows) and (maybe) C-literal-like emits.

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